Compounds

ABSTRACT

The present invention provides a compound of formula (I), and its use in methods of treatment, including the treatment of bacterial infections. Methods for the preparation of the compound of formula (I) are also provided. The compound of formula (I) has the structure shown below, where —R 6  and —R 7  are each together with the carbonyl group and nitrogen alpha to the carbon to which it is attached an amino acid residue, except that R6 together with the carbonyl group and nitrogen alpha to the carbon to which it is attached is not a phenylalanine, leucine or valine residue and/or —R 7  together with the carbonyl group and nitrogen alpha to the carbon to which it is attached is not a leucine, iso-leucine, phenylalanine, threonine, valine or nor-valine residue, and —T, A 1 , A 2 , A 3  and —R 10  are as discussed in the application:

RELATED APPLICATIONS

The present case is related to GB 1421020.7 filed on 26 Nov. 2014(26.11.2014) and GB 1516059.1 filed on 10 Sep. 2015 (10.09.2015), thecontents of both of which are hereby incorporated by reference in theirentirety.

FIELD OF THE INVENTION

The present invention relates to novel polymyxin compounds, combinationsof compounds, pharmaceutical compositions comprising the compounds andthe use of the compounds, pharmaceutical compositions and combinationsfor treatment, for example treatment of microbial infections,particularly by Gram-negative bacteria.

BACKGROUND

In susceptible individuals, certain Gram-negative bacteria such asEscherichia coli, Klebsiella pneumoniae, Pseudomonas aeruginosa andAcinetobacter baumanii can cause serious infections, such as pneumonia,urinary tract infections, skin and skin structure infections such aswound infections, ear infections, eye infections, intra-abdominalinfections, bacterial overgrowth in the gastrointestinal tract andbacteraemia/sepsis. The treatment of serious bacterial infections inclinical practice can be complicated by antibiotic resistance. Recentyears have seen a rise in infections by Gram-negative bacteria which areresistant to many types of antimicrobials including broad spectrumantibiotics such as aminoglycosides, cephalosporins and evencarbapenems. There is therefore a need to identify new antimicrobialsthat are effective against Gram-negative bacteria, in particular againstmultidrug resistant Gram-negative bacteria.

Polymyxins are a class of antibiotics produced by the Gram-positivebacterium Bacillus polymyxa. First identified in the late 1940s,polymyxins, particularly polymyxin B and polymyxin E (colistin, usuallyas its prodrug colistin methane sulphonate) were used in the treatmentof Gram-negative infections. However, these antibiotics exhibited sideeffects such as neurotoxicity and nephrotoxicity. Nevertheless thepolymyxins now play an important role in the therapy of MDRGram-negative infections due to the lack of viable alternatives.However, their use in therapy is limited to treatment of last resort.

WO 2008/017734 tries to address this toxicity problem by providingpolymyxin derivatives carrying at least two but no more than threepositive charges. These compounds are said to be effective antibacterialagents with reduced renal toxicity. It is hypothesised in the disclosurethat the reduced number of positive charges decreases the affinity ofthe compound for isolated rat kidney tissue which in turn may lead to areduction in nephrotoxicity.

Certain des-fatty acyl polymyxin derivatives have also been disclosedwith reduced acute toxicity in mice whilst retaining good activityagainst pseudomonads (Katsuma et al. Chem. Pharm. Bull. 2009; 57,332-336; Sato et al. Chem. Pharm. Bull. 2011; 59, 597-602). Thecompounds were significantly less active than polymyxin B against E.coli and K. pneumoniae.

WO 2010/075416 provides urea linked aryl polymyxin decapeptidesincluding CB182,804, which is reported to have similar activity butreduced renal toxicity compared with polymyxin B. Phenyl cyclopropanepolymyxin derivatives are also described in U.S. Pat. No. 8,415,307.These compounds are shown to have similar or reduced activity comparedwith polymyxin B.

WO 2012/168820 provides a further series of polymyxin derivativesreported to have reduced toxicity, and sometimes enhanced activitycompared with polymyxin B, in which the diaminobutyrate group atposition 3 in the tripeptide side chain is replaced by adiaminopropionate moiety.

WO 2015/149131 and Velkov et al. describe modified polymyxin compounds.Typically these compounds retain a fatty acyl group at the N terminal ofa polymyxin decapeptide, including, for example, an octanoyl or anonanoyl group.

There remains a need for less toxic polymyxin derivatives which offertherapeutic preparations with consistently potent activity across thetarget pathogens and acceptable toxicity.

The present inventors have previously described in WO 2013/072695, TW101142961 and GCC 2012/22819, the contents of each of which are herebyincorporated in their entirety, polymyxin compounds for use in thetreatment of microbial infections.

The present inventors have also described in WO 2014/188178 and WO2015/135976, the contents of both of which are hereby incorporated intheir entirety, alternative polymyxin compounds for use in the treatmentof microbial infections. In particular, WO 2014/188178 describesmodifications to the N terminal of polymyxin decapeptides andnonapeptides. WO 2015/135976 describes modifications to the N terminalof polymyxin nonapeptides.

Surprisingly, the present inventors have found certain polymyxinderivatives which have reduced toxicity compared to polymyxin orcolistin and are particularly active against

Gram-negative bacteria, including bacterial strains with decreasedsusceptibility to polymyxin B and/or and polymyxin E. These agents thusoffer therapeutic options of consistently potent activity, but lowertoxicity than currently available therapies.

SUMMARY OF THE INVENTION

In a general aspect the present invention provides a polymyxin compoundof formula (I) or formula (II), as described herein, and its use in amethod of treatment or prophylaxis, and optionally in combination with asecond agent (which may be referred to as an active agent). Thecompounds of formula (I) of formula (II) may be used to treat amicrobial infection, such as a Gram-negative bacterial infection.

In a first aspect of the invention, there is provided a compound offormula (I), and pharmaceutically acceptable salts and solvates thereof.The compound of formula (I) is represented thus:

wherein:

-T is R^(T)-X—;

-A¹- is absent or is an amino acid residue;

-A²- is an amino acid residue selected from threonine and serine, suchas L-threonine and L-serine;

-A³- is an amino acid residue represented by:

where the asterisk is the point of attachment to -A²-, and —R³ is C₁₋₆alkyl, such as C₁₋₄, having one amino or one hydroxyl substituent;

—X— is —C(O)—, —NHC(O)—, —OC(O)—, —CH2— or —SO₂—;

—RT is a terminal group containing hydroxyl and/or amino functionality,and where -A¹- is absent, R_(T)-X— is not an α-amino acid residue havinga free α-amino group (—NH₂), for example where the amino acid isselected from the group consisting of Ala, Ser, Thr, Val, Leu, Ile, Pro,Phe, Tyr, Trp, His, Lys, Arg, α,γ-diaminobutyric acid (Dab) andα,β-diaminopropionic acid (Dap);

—R⁶ together with the carbonyl group and nitrogen alpha to the carbon towhich it is attached is an amino acid residue;

—R⁷ together with the carbonyl group and nitrogen alpha to the carbon towhich it is attached is an amino acid residue;

and —R⁶ together with the carbonyl group and nitrogen alpha to thecarbon to which it is attached is not a phenylalanine, leucine or valineresidue and/or —R⁷ together with the carbonyl group and nitrogen alphato the carbon to which it is attached is not a leucine, iso-leucine,phenylalanine, threonine, valine or nor-valine residue;

R¹⁰ together with the carbonyl group and nitrogen alpha to the carbon towhich it is attached, is a threonine or leucine residue;

and salts, solvates, protected forms and/or prodrug forms thereof.

In one embodiment, the amino acid at position 6 is substituted withanother amino acid.

In one embodiment, the amino acid at position 7 is substituted withanother amino acid.

In one embodiment, where -A¹- is absent, R^(T)-X— is not an α-amino acidresidue, and in particular an α-amino acid residue having a free α-aminogroup (—NH₂).

In one embodiment, where -A¹- is absent, R^(T)-X— is not an an α-aminoacid residue selected from the group consisting of Ala, Ser, Thr, Val,Leu, Ile, Pro, Phe, Tyr, Trp, His, Lys, Arg, α,γ-diaminobutyric acid(Dab) and α,γ-diaminopropionic acid (Dap), where the α-amino acid has afree α-amino group (—NH₂).

In a second aspect of the invention, there is provided a compound offormula (II), and pharmaceutically acceptable salts and solvatesthereof. The compound of formula (II) is represented thus:

wherein:

-T^(A) is hydrogen, C₁₋₄ alkyl or R^(N)—X—;

-A¹- is absent or is an amino acid residue;

-A²- is absent or is an amino acid residue;

-A³- is absent or is an amino acid residue;

—X— is —C(O)—, —NHC(O)—, —OC(O)—, —CH₂— or —SO₂—; —R^(N) is a terminalgroup, such as a group —R^(T) as described herein;

—R^(6A) is C₁₋₁₂ alkyl, C₀₋₁₂ alkyl(C₃₋₁₀ cycloalkyl), C₀₋₁₂ alkyl(C₃₋₁₀heterocyclyl) or C₀₋₁₂ alkyl(C₅₋₁₀ aryl), where the C₁₋₁₂ alkyl, C₃₋₁₀cycloalkyl group C₃₋₁₀ heterocyclyl group, and the C₅₋₁₀ aryl group areoptionally substituted, and the optional substituents are as describedherein, and with the proviso that —R^(6A) is not benzyl, iso-butyl,iso-propyl, and optionally —R^(6A) is not methyl, phenyl,4-hydroxyphenyl, (1H-indol-3-yl) methyl, 4-phenylphen-1-yl methyl,—(CH₂)₇CH₃, 4—(OBn)-phen-1-yl methyl or —CH₂S(CH₂)₅CH₃

—R^(7A) together with the carbonyl group and nitrogen alpha to thecarbon to which it is attached is an amino acid residue;

R¹⁰ together with the carbonyl group and nitrogen alpha to the carbon towhich it is attached, is a threonine or leucine residue;

and salts, solvates, protected forms and/or prodrug forms thereof.

In a third aspect the invention provides a pharmaceutical compositioncomprising a compound of formula (I) or formula (II) and a biologicallyacceptable excipient, optionally together with a second active agent.

In a fourth aspect there is provided a compound of formula (I) orformula (II) or a pharmaceutical composition comprising the compound offormula (I) or formula (II) for use in a method of treatment.

The invention additionally provides a compound of formula (I) or formula(II) or a pharmaceutical composition comprising the compound of formula(I) or formula (II) for use in a method of treating a microbialinfection, such as a Gram-negative bacterial infection.

The present invention also provides a method of identifying usefulcombinations for therapy, the method comprising testing a combination ofa compound of formula (I) or formula (II) with a biologically activecompound and determining the biological efficacy of the combination, forexample with comparison to the biologically active compound alone and/orthe compound of formula (I) or formula (II).

In an alternative aspect, the compounds of formula (I) or formula (II)are suitable for use in the treatment of fungal infections, for examplein combination together with an antifungal agent.

In a further aspect of the invention there is provided a polymyxincompound of formula (I) or formula (II) for use in a method of treatmentor prophylaxis, in combination with an active agent.

Also provided are methods for preparing compounds of formula (I) andformula (II).

In one aspect of the invention there is provided a compound of formula(IV):

wherein:

—T^(A) is hydrogen, C₁₋₄ alkyl or R^(N)—X—;

-A¹- is absent or is an amino acid residue;

-A²- is absent or is an amino acid residue;

-A³- is absent or is an amino acid residue;

—X— is —C(O)—, —NHC(O)—, —OC(O)—, —CH₂— or —SO₂—;

—R^(N) is a terminal group, such as a group —R^(T) as described herein;

—R⁶ together with the carbonyl group and nitrogen alpha to the carbon towhich it is attached is an amino acid residue;

—R⁷ together with the carbonyl group and nitrogen alpha to the carbon towhich it is attached is an amino acid residue;

and one of —R⁶ and —R⁷ comprises a haloaryl group, such as a halophenylgroup, such as a bromopehnyl group;

R¹⁰ together with the carbonyl group and nitrogen alpha to the carbon towhich it is attached, is a threonine or leucine residue;

and salts, solvates, and/or protected forms thereof.

In one embodiment, one of one of —R⁶ and —R⁷ comprises a benzyl group,where the phenyl is substituted with halo, such as monosubstituted.

In one embodiment, one of —R⁶ and —R⁷ comprises a haloaryl group.

In one embodiment, one of —R⁶ and —R^(Z), comprises a bromoaryl group.

Other aspects of the invention are discussed in detail herein.

DETAILED DESCRIPTION OF THE INVENTION

The present invention provides compounds of formula (I) and formula (II)for use in medical treatment, particularly in combination with a secondagent.

Broadly, the compounds of formula (I) and formula (II) are polymyxincompounds carrying an amino acid substitution within the polypeptidecore. The N terminal of the polymyxin compound is optionally modified.

In the compounds of formula (I) the amino acid at position 6 and/or theamino acid at position 7 is substituted with another amino acid. Thus,the amino acid residue at position 6 and/or position 7 is not an aminoacid residue present in Polymyxin B or Colistin.

In the compounds of formula (II) the amino acid at position 6 issubstituted with another amino acid, and optionally the amino acid atposition 7 is also substituted. Thus, the amino acid residue at position6 and optionally position 7 is not an amino acid residue present inPolymyxin B or Colistin.

In both compounds (I) and (II) the amino acids at one or more ofpositions 1, 2, 3, and 10 are optionally substituted with another aminoacid. Thus, the amino acid residues at positions 1, 2, 3, and 10 may notbe amino acid residues that are present in Polymyxin B or Colistin. Theamino acids at positions 1, 2, and 3 may be optionally deleted.

The compound of formula (I) is a polymyxin compound having a modified Nterminal. For example, the compound has an N terminal group thatcontains one, two or three hydroxyl groups and/or one, two or threeamino groups. In addition to, or as an alternative to, the N terminalgroup has a nitrogen-containing heterocyclyl (or heterocyclylene) groupand/or a nitrogen-containing heteroalkylene group. The N terminal groupmay be a substituted alkyl group or may be or include an optionallysubstituted aryl, cycloalkyl or heterocyclyl group. The presence of ahydroxyl group or a basic amino group within the terminal group isassociated with particular advantages, as discussed below.

The compound of formula (II) is a compound where the N terminal isoptionally modified. Where the N terminal is modified, the terminalgroups may include those fatty acid groups that are found within theknown polymyxin series of compounds, such as Polymyxin B and Colistin,and other polymyxin compounds reported in the art, such as thosepolymyxin derivatives described in WO 2012/168820, WO 2013/072695 and WO2015/135976.

The N terminal group within the compounds of formula (II), wherepresent, may be the same as the N terminal group within the compounds offormula (I).

The compounds of formula (I) and formula (II) may have comparable orimproved biological activity compared to Polymyxin B or Colistin againstone or more of E. coli, P. aeruginosa, K. pneumonia, or A. baumanniibacterial strains. Such compounds are useful alternatives to thepolymyxin type compounds previously described in the art.

Furthermore, the present inventors have found that each compound offormula (I) and formula (II) is active against a broad range ofbacteria. In contrast the compounds previously described in the art havea varied profile of biological activity.

Some of the polymyxin compounds or polymyxin derivatives in the art areknown or suspected to have a poor toxicity profile. For example, the useof compounds having a fatty acyl chain at the N terminal, such asPolymyxin B and Colistin, is associated with nephrotoxicity. The use ofalternative N terminal group may therefore reduce toxicity. Thus, thecompounds of formula (I) include hydroxyl and/or amino functionalitywhich the inventors have shown is associated with a reduction intoxicity, especially a reduction in nephrotoxicity.

Vaara et al. (Antimicrob. Agents Chemother. 2008, 52, 3229) havesuggested that the pharmacological and toxicity properties of apolymyxin compound may be altered with changes to the polymyxinpolypeptide sequence. In particular, Vaara et al. have prepared apolymyxin compound having only three positive charges, whereas thepolymyxin B nonapeptide carries five positive charges.

In contrast the present inventors have shown that adaptations to the Nterminal of a polymyxin compound may reduce nephrotoxicity. As describedherein, the N terminal has a substituent containing a hydroxyl group oran amino group (which may be in the form of a nitrogen-containingheterocycle).

Furthermore, the compounds of formula (I) and formula (II) are believedto be capable of increasing the antimicrobial activity of a secondantimicrobial agent, such as rifampicin. Such combinations may havecomparable or improved biological activity compared to the combinationof the second agent with Polymyxin B or Colistin, for example againstone or more of E. coli, P. aeruginosa, K. pneumonia, or A. baumanniistrains. For example, compounds of formula (I) and formula (II) may havecomparable biological activity compared to Polymyxin B or Colistinagainst one or more of E. coli, P. aeruginosa, K. pneumonia, or A.baumannii strains.

Polymyxin Compounds of Formula (I)

The compounds of formula (I) are variants of Polymyxin B and are alsoN-terminal derivatives of the polymyxin series of compounds. The core ofthe compound of formula (I) is a variant of a polymyxin compound, suchas a variant of the polymyxin B decapeptide, nonapeptide (PMBN,Polymyxin 2-10), octapeptide or heptapeptide, where the amino acid atposition 6 and/or position 7 is substituted with another amino acid asdescribed herein, and optionally the amino acid residues at positions 1,2, 3 and 10 are substituted with another amino acid residue. Optionallythe amino acid residue at position 1 (-A¹-) may be deleted.

Further, the present inventors have also established that the groupattached to the N terminal of a polymyxin nonapeptide is an importantdeterminant of biological activity and compound toxicity. The inventorshave identified certain N terminal substituent groups that show enhancedactivity and/or exhibit less toxicity compared to Polymyxin B orColistin, for example as measured against HK-2 cells. The activity isassociated with the presence of amino functionality at specificlocations within the N terminal group. Further improvements in activityare also found where certain substituents are present in the N terminalgroup, and the chiral centres in the terminal group have a specificstereochemistry.

The inventors' earlier work relating to N terminal groups is included inthe present application for useful support to the present invention.Whilst the present invention is primarily focussed on new substitutionsat positions 6 and 7 of the polymyxin core, the variant polypeptide coremay be used together with the N terminal group modifications describedin the inventors' earlier work, such as described in WO 2013/072695,PCT/GB2014/051547 (published as WO 2014/188178) and GB 1404301.2, andmost particularly as described in PCT/GB2014/051547 and in GB 1404301.2.

The variant polypeptide core may be used together with the N terminalgroup modifications described in the inventors' earlier work, such asdescribed in WO 2015/135976, which claims priority to GB 1404301.2.Thus, the group —R¹⁵ described in WO 2015/135976 may be used as a group—R^(T) in the present case.

Substitutions and deletions within the polypeptide sequence of thepolymyxin compounds are known.

For example, the presence of the Dab amino acid residue at position 1 ofPolymyxin B was not believed to be important for activity, and thisamino acid is often absent from polymyxin derivatives described in theprior art. See, for example, WO 2008/017734 and WO 2009/098357, wherethe amino acid residue at position 1 is absent. Similarly, Okimura etal. dispense with the amino acid residue at position 1, providinginstead an aminocyclohexylcarbonyl substituent at the N terminal of theamino acid residue at position 2.

The present inventors have also described polymyxin nonapeptide formswhere the amino acid residue at position 1 is absent, and the N terminalof the amino acid reside at position 2 is modified. See, for example, WO2013/072695.

WO 2012/168820 describes the substitution of the (S)-Dab amino acidresidue at position 3 of Polymyxin B with (S)-Dap. The authors explainthat this substitution provides compounds having reduced cytotoxicity inhuman renal cells and improved antibacterial activity, for exampleagainst P. aeruginosa, K. pneumonia, and/or A. Baumannii.

WO 2012/168820 suggests that other positions in the polymyxinpolypeptide sequence may be modified, such as at positions 6 and 7.

Substitutions and deletions of the amino acids at positions 1, 2 and 3are also described. The work in WO 2008/017734 and WO 2009/098357describes the changes in biological activity that are associated withthe changes in the amino acid residues at positions 1, 2 and 3.

The present invention provides a compound of formula (I) and the use ofthis compound in a method of treatment. The compound of formula (I) isrepresented thus:

wherein:

—T is R^(T)—X—;

-A¹- is absent or is an amino acid residue;

-A²- is an amino acid residue selected from threonine and serine, suchas L-threonine and L-serine;

-A³- is an amino acid residue represented by:

where the asterisk is the point of attachment to -A²-, and —R³ is C₁₋₆alkyl, such as C₁₋₄, having one amino or one hydroxyl substituent;

—X— is —C(O)—, —NHC(O)—, —OC(O)—, —CH₂— or —SO₂—;

—R^(T) is a terminal group containing hydroxyl and/or aminofunctionality, and where -A¹- is absent, R^(T)—X— is not an α-amino acidresidue having a free α-amino group (—NH₂), for example where theα-amino acid residue is selected from the group consisting of Ala, Ser,Thr, Val, Leu, Ile, Pro, Phe, Tyr, Trp, His, Lys, Arg,α,γ-diaminobutyric acid (Dab) and α,β-diaminopropionic acid (Dap);

—R⁶ together with the carbonyl group and nitrogen alpha to the carbon towhich it is attached is an amino acid residue;

—R⁷ together with the carbonyl group and nitrogen alpha to the carbon towhich it is attached is an amino acid residue;

and —R⁶ together with the carbonyl group and nitrogen alpha to thecarbon to which it is attached is not a phenylalanine, leucine or valineresidue and/or —R⁷ together with the carbonyl group and nitrogen alphato the carbon to which it is attached is not a leucine, iso-leucine,phenylalanine, threonine, valine or nor-valine residue;

R¹⁰ together with the carbonyl group and nitrogen alpha to the carbon towhich it is attached, is a threonine or leucine residue;

and salts, solvates, protected forms and/or prodrug forms thereof.

—R⁶ and —R⁷

In one embodiment, —R⁶ together with the carbonyl group and nitrogenalpha to the carbon to which it is attached is a phenylalanine, leucineor valine residue. In this embodiment, the group —R⁷ together with thecarbonyl group and nitrogen alpha to the carbon to which it is attachedis not a leucine, iso-leucine, phenylalanine, threonine, valine ornor-valine residue.

In one embodiment, —R⁶ together with the carbonyl group and nitrogenalpha to the carbon to which it is attached is not a phenylalanine,leucine or valine residue. Additionally or alternatively, —R⁶ togetherwith the carbonyl group and nitrogen alpha to the carbon to which it isattached is not an alanine, tyrosine, tryptophan or phenylglycineresidue. Thus, the amino acid residue present at the 6-position may beregarded as a replacement to the amino acid residues at that position ofthe polymyxin core.

In one embodiment, —R⁷ together with the carbonyl group and nitrogenalpha to the carbon to which it is attached is a leucine, iso-leucine,phenylalanine, threonine, valine or nor-valine residue. In thisembodiment, —R⁶ together with the carbonyl group and nitrogen alpha tothe carbon to which it is attached is not a phenylalanine, leucine orvaline residue.

In one embodiment, —R⁷ together with the carbonyl group and nitrogenalpha to the carbon to which it is attached, is an α-amino acid residue,such as a proteinogenic amino acid residue, so long as the amino acidresidue is not a leucine, iso-leucine, phenylalanine, threonine, valineor nor-valine residue.

In one embodiment, —R⁶ together with the carbonyl group and nitrogenalpha to the carbon to which it is attached, is an α-amino acid residue,such as a proteinogenic amino acid residue, so long as the amino acidresidue is not a phenylalanine, leucine or valine residue.

In one embodiment, —R⁶ together with the carbonyl group and nitrogenalpha to the carbon to which it is attached, is an amino acid residueselected from the group consisting of Leu, OctGly, BipAla, Tyr,norvaline, and norleucine, and for example the D-forms thereof.

In one embodiment, —R⁷ together with the carbonyl group and nitrogenalpha to the carbon to which it is attached in an amino acid residueselected from the group consisting of leucine, OctGly, BipAla,Cys(S-Hex) and Cys(S-Bzl), and for example the L-forms thereof.Additionally or alternatively, —R⁷ together with the carbonyl group andnitrogen alpha to the carbon to which it is attached in an amino acidresidue selected from the group consisting of alanine, threonine,serine, valine, 2-aminobutyric acid (Abu) and 2-aminoisobutyric acid(Aib), and for example the L-forms thereof.

Alternatively, —R⁷ together with the carbonyl group and nitrogen alphato the carbon to which it is attached in an amino acid residue selectedfrom the group consisting of alanine, phenylalanine, threonine, serine,valine, 2-aminobutyric acid (Abu) and 2-aminoisobutyric acid (Aib), andfor example the L-forms thereof.

In one embodiment, —R⁷ together with the carbonyl group and nitrogenalpha to the carbon to which it is attached is a leucine residue, suchas L-leucine. In this embodiment, the amino acid residue at the7-position is not substituted with reference to the amino acid residueat the 7-position of Polymyxin B.

In one embodiment, the α-amino acid residue at position 6 or position 7is not a proteinogenic amino acid residue.

In one embodiment, the α-amino acid residue does not contain hydroxyl(—OH) or amino (—NH₂) functionality in its side chain (i.e. the group—R⁶ does not contain a hydroxyl group or an amino group). Optionally,the α-amino acid residue does not contain thiol (—SH) functionality inits side chain (i.e. the group —R⁶ does not contain a thiol group).

In one embodiment, the amino acid residue at position 6 is an L- orD-amino acid residue, such as a D-amino acid residue. In one embodiment,the amino acid residue at position 7 is an L- or D-amino acid residue,such as an L-amino acid residue.

Where position 6 has a D-amino acid residue and position 7 has anL-amino acid residue, the structure of the compound of formula (I) is:

In one embodiment, the compound of formula (I) is the compound as shownabove.

In one embodiment, a group —R⁶ or a group —R⁷ is a group —R^(6A) asdefined below.

For example, in one embodiment, —R⁶ and/or —R⁷ is C₁₋₁₂ alkyl, C₀₋₁₂alkyl(C₃₋₁₀ cycloalkyl), C₀₋₁₂ alkyl (C₃₋₁₀ heterocyclyl) or C₀₋₁₂alkyl(C₅₋₁₀ aryl), where the C₁₋₁₂ alkyl, C₃₋₁₀ cycloalkyl group C₃₋₁₀heterocyclyl group, and the C₅₋₁₀ carboaryl group are optionallysubstituted.

In one embodiment, the group —R⁶ is not benzyl, iso-butyl or iso-propyl(the residue at position 6 may not be phenylalanine, leucine or valine).

In one embodiment, the group —R⁶ is not 4-phenylphen-1-yl methyl or—CH₂S(CH₂)₅CH₃. The C₁₋₁₂ alkyl group, C₃₋₁₀ cycloalkyl group, C₃₋₁₀heterocyclyl group, and the C₅₋₁₀ aryl group may be substituted with oneor more groups —R^(z), where each group —R^(Z) is selected from halo,optionally substituted C₁₋₁₂ alkyl, optionally substituted C₂₋₁₂alkenyl, optionally substituted C₂₋₁₂ alkynyl, optionally substitutedC₃₋₁₀ cycloalkyl, optionally substituted C₃₋₁₀ heterocyclyl, optionallysubstituted C₅₋₁₂ aryl, —CN, —NO₂, —OR^(Q), —SR^(Q), —N(R^(w))C(O)R^(Q),—N(R^(Q))₂, and —C(O)N(R^(Q))₂,

-   -   where —R^(w) is H or C₁₋₄ alkyl; and    -   —R^(Q) is H or —R^(Q1), and —R^(Q1) is selected from optionally        substituted C₁₋₁₂ alkyl, C₂₋₁₂ alkenyl, C₂₋₁₂ alkynyl, and C₅₋₁₂        aryl,

and in a group —N(R^(Q))₂ the groups —R^(Q) may together with thenitrogen atom to which they are attached form a C₅₋₆ heterocycle, wherethe heterocycle is optionally substituted,

-   -   with the proviso that C₁₋₁₂ alkyl is not substituted with alkyl,        alkenyl or alkynyl.

In one embodiment, —R⁶ and/or —R⁷ is optionally substituted C₁₋₁₂ alkyl.

In one embodiment, —R⁶ and/or —R⁷ is optionally substituted C₁₋₁₂ alkyl,where the C₁₋₁₂ alkyl is optionally substituted with one or more groupsselected from halo, such as fluoro, optionally substituted C₃₋₁₀cycloalkyl, optionally substituted C₃₋₁₀ heterocyclyl, optionallysubstituted C₅₋₁₂ aryl, —CN, —NO₂, —OR^(Q), —SR^(Q), —N(R^(w))C(O)R^(Q),—N(R^(Q))₂, and —C(O)N(R^(Q))₂.

An alkyl group is typically a C₁₋₁₂ alkyl group, such as C₂₋₁₂ alkyl,such as C₄₋₁₂ alkyl, such as C₅₋₁₂ alkyl, such as C₆₋₁₂ alkyl, such asC₈₋₁₂ alkyl, for example C₂₋₁₀ alkyl, C₄₋₁₀ alkyl, C₅₋₁₀ alkyl and C₆₋₁₀alkyl.

Additionally or alternatively, an alkyl group may be C₃₋₁₂ alkyl, suchas C₃₋₁₀ alkyl. The alkyl group may be linear or branched.

Where the alkyl group is substituted, it may be monosubstituted. Asubstituent may be provided at a terminal of the alkyl group.

In one embodiment, —R⁶ and/or —R⁷ is C₁₋₁₂ alkyl substituted withalkylthio or arylalkylthio. Compounds containing an amino acid residueat position 7 with this functionality are described by Velkov et al.

In one embodiment, —R⁶ and/or —R⁷ is C₁₋₁₂ alkyl substituted withalkylthio, such as C₁₋₁₂ alkylthio.

In one embodiment, the alkylthio is C₆ alkylthio.

In one embodiment, —R⁶ and/or —R⁷ is arylalkylthio, such as C₅₋₁₀aryl—C₁₋₁₂ alkylthio, such as phenyl—C₁₋₁₂ alkylthio, such asphenyl—C₁₋₁₂ alkylthio.

In one embodiment, the arylalkylthio is benzylthio (PhCH₂S—).

In one embodiment, —R⁷ is C₃ or C₄ alkyl.

In one embodiment, —R⁷ is n-propyl.

A C₀₋₁₂ alkyl group, such as present in the groups C₀₋₁₂ alkyl(C₃₋₁₀cycloalkyl), C₀₋₁₂ alkyl(C₃₋₁₀ heterocyclyl) and C₀₋₁₂ alkyl(C₅₋₁₀aryl), may be a C₁₋₁₂ alkyl group. References to an alkyl group here areunderstood to refer to an alkylene linker.

A C₀₋₁₂ alkyl group may be C₁₋₁₂ alkyl, such as C₁₋₆ alkyl, such as C₁₋₄alkyl, such as C₁₋₂ alkyl, such as —CH₂— and —CH₁CH₂—, such as —CH₂—.

A C₀₋₁₂ alkyl group may be C₁₋₁₂ alkyl such as C₆₋₁₂ alkyl, such asC₆₋₁₀ alkyl. The C₀₋₁₂ alkyl group may be absent i.e. C₀₋₁₂ alkyl groupmay be C₀.

In one embodiment, —R⁶ and/or —R⁷ is C₀₋₁₂ alkyl(C₃₋₁₀ cycloalkyl),where the C₃₋₁₀ cycloalkyl is optionally substituted.

The C₃₋₁₀ cycloalkyl may be a C₅₋₇ cycloalkyl group, such as C₅₋₆cycloalkyl group.

In one embodiment, C₃₋₁₀ cycloalkyl is cyclopentyl or cyclohexyl, suchas cyclohexyl.

A cycloalkyl group may be optionally substituted, such as optionallymonosubstituted.

Where, the cycloalkyl group is cyclohexyl, the cyclohexyl is optionallysubstituted at the 2- or 4-position, such as the 4-position.

In one embodiment, —R⁶ and/or —R⁷ is C₁ alkyl(C₆ cycloalkyl). Here, theamino acid residue formed from —R⁶ and/or —R⁷ together with the carbonylgroup and nitrogen alpha to the carbon to which it is attached may bereferred to as cyclohexylalanine.

In one embodiment, —R⁷ is cyclohexyl (C₆ cycloalkyl). Here, the aminoacid residue formed from —R⁷ together with the carbonyl group andnitrogen alpha to the carbon to which it is attached may be referred toas cyclohexylglycine.

In one embodiment, —R⁶ is C₁ alkyl(C₆ cycloalkyl).

In one embodiment, —R⁷ is C₁ alkyl(C₆ cycloalkyl).

In one embodiment, —R⁶ and/or —R⁷ is not —(CH₂)₄-cycicohexyl.

In one embodiment, —R⁶ and/or —R⁷ is not —(C₆H₁₀)—Pr, such as where the—Pr group is a linear propyl group.

In one embodiment, —R⁶ and/or —R⁷ is C₀₋₁₂ alkyl(C₅₋₁₀ aryl), where theC₅₋₁₀ aryl is optionally substituted.

It is preferred that an aryl group, where present, is a carboaryl group.The inventors have found that the carboaryl is associated with anincrease antimicrobial effect compared with heteroaryl functionality.

In one embodiment, —R⁶ and/or —R⁷ is substituted C₀₋₁₂ alkyl(C₅₋₁₀aryl).

In one embodiment, —R⁶ and/or —R⁷ is substituted benzyl (—CH₂Ph). Thebenzyl group may be substituted on the phenyl ring, such as only on thephenyl ring.

In one embodiment, —R⁶ and/or —R⁷ is monosubstituted benzyl.

In one embodiment, —R⁶ and/or —R⁷ is monosubstituted benzyl, where thephenyl group is substituted at the 2-, 3- or 4-position, such as the 2-or 4-position, such as the 4-position.

As noted above, C₁₋₁₂ alkyl group, C₃₋₁₀ cycloalkyl group, C₃₋₁₀heterocyclyl group, and the C₅₋₁₀ aryl group may be substituted with oneor more groups —R^(z). Examples of —R⁷ include optionally substitutedalkyl, alkenyl, alkynyl, cycloalkyl, aryl and heterocycle groups.

Where a group, such as alkyl, alkenyl, alkynyl, cycloalkyl, aryl andheterocycle, is optionally substituted, the group may have one or moresubstituent groups selected from halo, haloalkyl, alkyl, alkenyl,alkynyl, and aryl, except that alkyl alkenyl, and alkynyl groups are notsubstituents to the alkyl alkenyl, and alkynyl groups.

The optional substituents may include groups such as -13 OR^(Q),—SR^(Q), —N(R^(w))C(O)R^(Q), —N(R^(Q))₂, and —C(O)N(R^(Q))₂.

In one embodiment, each —R^(Q) is —R^(Q1). Thus, hydroxyl (—OH) andprimary amino functionality (—NH₂) is not present.

An aryl group may be a carboaryl group, such as C₆₋₁₀ carboaryl, or aheteroaryl group, such as C₅₋₁₀ heteroaryl.

In one embodiment, a reference to aryl is a reference to phenyl.

A haloalkyl group is an alkyl group, such as described above, having oneor more halo substituents. The haloalkyl group may be a perhaloalkylgroup. In one embodiment, a haloalkyl group is —CF₃.

An alkenyl group is typically a C₂₋₁₂ alkenyl, such as C₄₋₁₂ alkenyl,such as C₅₋₁₂ alkenyl, such as C₆₋₁₂ alkenyl, for example C₂₋₁₀ alkenyl,C₄₋₁₀ alkenyl, C₆₋₁₀ alkenyl and C₆₋₁₀ alkenyl.

An alkynyl group is typically a C₂₋₁₂ alkynyl, such as C₄₋₁₂ alkynyl,such as C₆₋₁₂ alkynyl, such as C₆₋₁₂ alkynyl, for example C₂₋₁₀ alkynyl,C₄₋₁₀ alkynyl, C₅₋₁₀ alkynyl and C₆₋₁₀ alkynyl.

An alkyl, alkenyl or alkynyl group may be a linear or branched group.

In one embodiment, the alkyl, alkenyl or alkynyl group is unsubstituted.

A cycloalkyl group is typically C₃₋₁₀ cycloalkyl may be a C₅₋₇cycloalkyl group, such as C₅₋₆ cycloalkyl group.

In one embodiment, C₃₋₁₀ cycloalkyl is cyclopentyl or cyclohexyl, suchas cyclohexyl.

A group —R^(Z) may be halo, such as bromo.

A group —R^(Z) may be alkyl, such as C₁₋₁₂ alkyl, such as C₂₋₁₂ alkyl,such as C₄₋₁₂ alkyl, such as C₅₋₁₂ alkyl, such as C₆₋₁₂ alkyl, forexample C₂₋₁₀ alkyl, C₄₋₁₀ alkyl, C₅₋₁₀ alkyl and C₆₋₁₀ alkyl.

The alkyl group may be a linear or branched alkyl group.

A group —R^(Z) may be aryl, such as carboaryl, such as C₆₋₁₀ carboaryl,or heteroaryl, such as C₅₋₁₀ heteroaryl. A group —R^(Z) may be phenyl.The aryl group may be substituted with one or more, such as one,substituent groups. In one embodiment, the aryl group is substitutedwith halo, haloalkyl, alkyl and aryl.

In one embodiment, —R⁶ and/or —R⁷ is benzyl, where the phenyl group issubstituted at the 2- or 4-postion, such as the 4-position, with phenyl(i.e. forming a biphenyl group).

In one embodiment, —R⁶ and/or —R⁷ is benzyl, where the phenyl group issubstituted at the 2- or 4-postion, such as the 4-postion, with alkyl,such as C₁₋₁₂ alkyl.

In one embodiment, —R⁶ and/or —R⁷ is benzyl, where the phenyl group issubstituted at the 2-, 3- or 4-postion, such as the 2- or 4-postion,such as the 4-position, with halo, such as bromo. In one embodiment, —R⁶and/or —R⁷ is benzyl, where the phenyl group is substituted at the 2- or4-postion, such as the 4-postion, with cycloalkyl, such as C₆cycloalkyl.

In one embodiment, —R⁶ and/or —R⁷ is not 4-hydroxyphenylmethyl (i.e. —R⁶together with the carbonyl group and nitrogen alpha to the carbon towhich it is attached is not a tyrosine residue).

The comments above refer to compounds where the a amino acid residue atposition 6 or position 7 has an α carbon atom that is substituted with—R⁶ and —H, or —R⁷ and —H. The —H may also be a site for substitution,providing di-substituted α amino acid residues at position 6 and/orposition 7.

In an alternative embodiment, the α carbon atom within the α amino acidresidue at position 6 and/or position 7 is di-substituted, where eachsubstituent is a group —R⁶ or —R⁷ as described herein.

In an alternative embodiment, the a carbon atom within the a amino acidresidue at position 6 and/or 7 is di-substituted, where each substituentis a group —R⁶ or —R⁷ as appropriate, where the groups —R⁶ may togetherwith the a carbon atom to which they are attached form a C₄₋₆ carbocycleor a C₅₋₆ heterocycle, and/or the groups —R⁷ may together with the αcarbon atom to which they are attached form a C₄₋₆ carbocycle or a C₅₋₆heterocycle, wherein the carbocycle and the heterocycle are optionallysubstituted with one or more groups —R^(z), as described above. Thecarbocycle is a cycloalkyl group as described herein. The heterocycle isa heterocyclyl group as described herein.

Where a heterocycle is present the heteroatom of the heterocyclyl groupis not provided at the β position (i.e. the heteroatom is not connectedto the α carbon).

The heterocycle contains a heteroatom selected from N, O and S, andoptionally contains further heteroatoms. A reference to N is a referenceto a group —NH— within a heterocycle, and a reference to S is —S—,—S(O)— or —S(O)₂—.

In one embodiment, —R⁶ and/or —R⁷ together with the carbonyl group andnitrogen alpha to the carbon to which it is attached is an amino havinga piperidine side chain that is a gem di-substituent to the α-carbon.Thus the α-carbon is a ring atom in the piperidine ring. This is acyclic analogue of Dab.

—R¹⁰

The —R¹⁰ position corresponds to amino acid position 10 in the polymyxincompounds. In one embodiment —R¹⁰ together with the carbonyl group andnitrogen alpha to the carbon to which it is attached is a threonineresidue, such as L-threonine.

-A¹-, -A²- and -A³-

In one embodiment, -A¹- is absent, and -A²- and -A³- are present. Such acompound may be referred to as a nonapeptide. Nonapeptide forms ofPolymyxin B and E are well known in the art.

In one embodiment, -A¹-, -A²- and -A³- are present. Such a compound maybe referred to as a decapeptide, and are based on, for example,deacylated decapeptide forms of Polymyxin B, E and M. Deacylated formsof Polymyxin B, E and M are well known in the art. Alternativedecapeptides may be prepared from a nonapeptide or heptapeptide byappropriate coupling of an amino acid/s to the N terminal of thenonapeptide or heptapeptide. It is noted that the deacylated formPolymyxin M would appear to be identical to that reported for PolymyxinA by Cubist (see WO 2010/075416 and U.S. Pat. No. 8,415,307).

It is noted that the compounds of the invention differ from Polymyxin B,E and M, and their deacylated forms, for at least the reason that theamino acid residue at position 6 and/or position 7 differs from theamino acid residue present in Polymyxin B, E and M.

The compounds of the invention, such as the compounds of formula (I) mayalso differ from Polymyxin B, E and M in the nature of the N terminalgroup. Polymyxins B, E and M have an fatty acid (fatty acyl) group atthe N terminal. In contrast, the compounds of formula (I) have aterminal group with hydroxyl and/or amino functionality.

The group -A¹- may be an α-amino acid.

A reference to an α-amino acid includes proteinogenic (“natural”)α-amino acids, optionally together with other α-amino acids.

Examples of α-amino acids that are not proteinogenic are those aminoacids generated by post-translational modification, or by other means.Examples include Dab, Dap, Dgp (α,β-diguanidinopropanoyl), ornithine andnor-valine

Also included are amino having a piperidine side chain that is a gemdi-substituent to the α-carbon. Thus the α-carbon is a ring atom in thepiperidine ring. This is a cyclic analogue of Dab.

In one embodiment, -A¹- is an amino acid residue.

In one embodiment, -A¹- is an α-amino acid residue.

In one embodiment, -A¹- is an amino acid selected from the groupconsisting of Lys, Arg, Dap, Ser, Thr, Ile, Tyr, His, Phe, Pro, Trp,Leu, Ala, Dab, Dap, Dgp (α,β-diguanidinopropanoyl), ornithine andnor-valine, including L- and D-forms thereof.

In one embodiment, -A¹- is an amino acid selected from the groupconsisting of Dab, Pro, Dap, Gly, Ser, His, Phe, Arg, Tyr, and Leu,including L- and D-forms thereof.

In one embodiment, -A¹- is a D α-amino acid.

In one embodiment, -A¹- is an L α-amino acid.

In one embodiment, -A¹- is a β-amino acid.

The compounds of the invention where -A¹- is an amino acid may beprepared from deacylated forms by appropriate derivatisation of the Nterminal.

In one embodiment, -A¹- is selected from Lys, Arg, Dap, Ser, Phe, Trp,Leu, Ala, Dab, Dap, ornithine or nor-valine, including L- and D-formsthereof.

In one embodiment, -A¹- is selected from Thr, Ser, Lys, Dab or Dap, forexample L-Thr, L-Ser, L-Lys, L-Dab or L-Dap.

In one embodiment, -A¹- is Dab, such as L-Dab.

In an alternative embodiment, where -A¹- is an amino acid it is not Dab,for example it is not L-Dab.

In one embodiment, -A²- is an amino acid residue selected from threonineand serine, such as L-threonine and L-serine.

In one embodiment, -A³- is an amino acid residue represented by:

where the asterisk is the point of attachment to -A²-, and —R³ is C₁₋₆alkyl, such as C₁₋₄ alkyl, having one amino or one hydroxyl substituent.The amino acid residue may be an L-form.

In one embodiment, —R³ has one amino substituent.

In one embodiment, —R³ has one hydroxyl substituent.

The amino group may be —NH₂, —NHMe or —NHEt. In one embodiment, theamino group is —NH₂.

In one embodiment, —R³ together with the carbonyl group and nitrogenalpha to the carbon to which it is attached, is α,γ-diaminobutyric acid(Dab), a serine residue, a threonine residue, a lysine residue, anornithine residue, or α,β-diaminopropionic acid (Dap).

In one embodiment, —R³ together with the carbonyl group and nitrogenalpha to the carbon to which it is attached, is α,γ-diaminobutyric acid(Dab), a serine residue, a lysine residue, or α,β-diaminopropionic acid(Dap).

In one embodiment, —R³ together with the carbonyl group and nitrogenalpha to the carbon to which it is attached, is α,γ-diaminobutyric acid(Dab) or α,β-diaminopropionic acid (Dap), such as L-Dab or L-Dap.

In one embodiment, —R³ together with the carbonyl group and nitrogenalpha to the carbon to which it is attached, is α,γ-diaminobutyric acid(Dab) or α,β-diaminopropionic acid (Dap), such as L-Dab or L-Dap.

In one embodiment, —R³ together with the carbonyl group and nitrogenalpha to the carbon to which it is attached, is a lysine residue, suchas L-Lys.

In one embodiment, —R³ together with the carbonyl group and nitrogenalpha to the carbon to which it is attached, is Dab, such as L-Dab.

Compounds of the invention where —R³ is a Dab side chain are obtainablefrom compounds such as Polymyxin B. Compounds where —R³ is a Dap sidechain may be prepared using the methods described in WO 2012/168820.Compounds where —R³ is a serine side chain may be prepared using themethods described by Vaara et al. (see, for example, Antimicrob. AgentsChemother. 2008, 52, 3229).

—X—

The group —X— may be selected from —NHC(O)—, —C(O)—, —OC(O)—, —CH₂— and—SO₂—.

In one embodiment —X— is selected from —C(O)—, —SO₂— and —CH₂—.

In one embodiment —X— is —C(O)—.

In one embodiment —X— is —SO₂—.

In one embodiment —X— is —CH₂—.

The right-hand side of the group —X— is the point of attachment to NH,the amino terminal of an amino acid residue, such as -A¹-, -A²- or -A³-.The left-hand side of the group —X— is the point of attachment to agroup such as —R^(T) (or —R^(N) for the compounds of formula (II).

—R⁷

The group —R^(T) together with —X— is an N terminal modification of thepolymyxin. The group —R^(T) contains hydroxyl and/or aminofunctionality.

In one embodiment, R^(T)—X— is not an α-amino acid residue, andspecifically R^(T)—X— is not an α-amino acid residue having a free amineN terminal i.e. a group —NH₂ that is attached to the a carbon of theamino acid residue. For example, R^(T)—X— is not an α-amino acid residuewhen -A¹- is absent. In one embodiment, R^(T)—X— is not an α-amino acidresidue when -A¹- is present. The amino acid may be selected from thegroup consisting of Ala, Ser, Thr, Val, Leu, Ile, Pro, Phe, Tyr, Trp,His, Lys, Arg, α,γ-diaminobutyric acid (Dab) and α,β-diaminopropionicacid (Dap).

The group —R^(T) may contain one, two or three hydroxyl groups, —OH.

The group —R^(T) may contain one, two or three amino groups,—NR_(A)-R^(B), where each —R^(A) is independently hydrogen or C₁₋₄alkyl, each —R^(B) is independently hydrogen or C₁₋₄ alkyl, or—NR^(A)-R^(B) is a guanidine group.

The group —R^(T) may contain one, two or three amino groups, where suchamino groups are present within a nitrogen-containing heterocycle, suchas azetidine, pyrrolidinyl, piperidinyl, piperazinyl or morpholinyl, ora nitrogen-containing heteroalkyl group.

The group —R^(T) may contain both hydroxyl and amino functionality.

In one embodiment, —R^(T) is not amino-substituted cyclohexyl, forexample when —X— is —C(O)—.

The compounds of formula (I) do not encompass the deacylated versions ofPolymyxin B (Deacylpolymyxin B-DAPB), D, E (Deacylcolistin-DAC) or M, orCirculin A. The compounds of formula (I) do not encompass thenonapeptide versions of Polymyxin B (PMBN), D, E or M, or Circulin A.

In one embodiment, R^(T)—X— is not an α-amino acid residue. An α-aminoacid residue is a group where —X— is —C(O)— and —R^(T) has a group—NR^(A)R^(B) (such as —NH₂) as a substituent to the carbon atom that isa to the group —X—.

A reference to an α-amino acid may be a reference to a proteinogenic(“natural”) α-amino acid, optionally together with other α-amino acids.

Examples of α-amino acids that are not proteinogenic are those aminoacids generated by post-translational modification, or by other means.Examples include Dab, Dap, Dgp (α,β-diguanidinopropanoyl), ornithine andnor-valine.

In one embodiment, R^(T)—X— is not Thr, Ser, α,γ-diaminobutyric acid(Dab) or α,β-diaminopropionic acid (Dap) residues.

In one embodiment, for example where the core of the compound of formula(I) is Polymyxin B, R^(T)—X— is not a Lys, Arg, Dap, Ser, Phe, Trp, Leuor Ala residue. In one embodiment, R^(T)—X— is not a Lys, Arg, Dap, Ser,Phe, Trp, Leu, Ala, Glu, α,γ-diaminobutyric acid (Dab) orα,β-diaminopropionic acid (Dap) residue.

In one embodiment, R^(T)—X— is not an Ala, Ser, Thr, Val, Leu, Ile, Pro,Phe, Tyr, Trp, His, Lys, Glu, or Arg residue.

In one embodiment, R^(T)—X— is not an Ala, Ser, Thr, Val, Leu, Ile, Pro,Phe, Tyr, Trp, His, Lys, Glu, Arg, α,γ-diaminobutyric acid (Dab) orα,β-diaminopropionic acid (Dap) residue.

In one embodiment, R^(T)—X— is not a proteinogenic (“natural”) α-aminoacid residue or a α,γ-diaminobutyric acid (Dab) or α,β-diaminopropionicacid (Dap) residue.

References to the amino acids above, may be a reference to the L- orD-form, such as the L-form.

In one embodiment, —R^(T) is not diaminophenyl, such as3,5-diaminophenyl, for example when —X— is —C(O)—.

Examples of —R^(T)

The present inventors have previously described the modification of theN terminal group of polymyxin nonapeptide compounds, such as N terminalmodifications to PMBN.

This work is described in WO 2013/072695, the contents of which arehereby incorporated by reference in their entirety.

The group —R^(T) may be additionally or alternatively selected from theN terminal groups of PCT/GB2014/051547 and/or GB 1404301.2, the contentsof which are hereby incorporated by reference in their entirety.

In one embodiment, —R^(T) is not a group selected from the terminalgroups of WO 2013/072695.

Terminal Groups of WO 2013/072695

The terminal group —R^(T) in the present case may be a group —R⁵ asdescribed in WO 2013/072695.

Thus, in one embodiment, and for example where -A¹- is absent, —R^(T) isselected from the group consisting of C₀₋₁₂ alkyl(C₄₋₆ nitrogenheterocyclyl), or C₂₋₁₂ alkyl or C₀₋₁₂ alkyl(C₃₋₈ cycloalkyl) whereinthe alkyl or cycloalkyl bears (i) one, two or three hydroxyl groups; or(ii) one —NR^(A)R^(B) group; or (iii) one —NR^(A)R^(B) group and one ortwo hydroxyl groups. In one embodiment, —R^(T) is not a group selectedfrom this list, for example where -A¹- is absent.

The C₀₋₁₂ alkyl group is an alkylene spacer linking the nitrogenheterocyclyl or cycloalkyl to —X—.

The spacer may be absent (this is C₀).

The C₀₋₁₂ alkyl group may be C₀₋₆ alkyl or C₀₋₄ alkyl, or C₁₋₁₂ alkyl,such as C₁₋₆, such as C₁₋₄ alkyl. The alkyl group may be linear orbranched, such as linear.

In one embodiment, —R^(T) is C₀₋₁₂ alkyl(C₄₋₆ nitrogen heterocyclyl).

The C₄₋₆ nitrogen heterocyclyl is a saturated carbocyclic ringcomprising at least one nitrogen ring atom, for example 1 or 2 nitrogenring atoms, such as only 1 nitrogen ring atom and optionally containinga further ring heteroatom selected from oxygen and sulfur.

Examples of C₄₋₆ heterocyclyl groups include azetidine, pyrrolidinyl,piperidinyl, piperazinyl and morpholinyl, such as azetidine,pyrrolidinyl and piperidinyl.

In one embodiment the heterocyclyl is linked to the remainder of themolecule through nitrogen. In the term “C₄₋₆ heterocyclyl”, theexpression C₄₋₆ represents the total number of ring atoms, includingcarbon and heteroatoms.

In one embodiment, —R^(T) is C₂₋₁₂ alkyl or C₀₋₁₂ alkyl(C₃₋₈ cycloalkyl)wherein the alkyl or cycloalkyl bears (i) one, two or three hydroxylgroups; or (ii) one —NR^(A)R^(B) group; or (iii) one —NR^(A)R^(B) groupand one or two hydroxyl groups.

In one embodiment, —R^(T) is C₂₋₁₂ alkyl, substituted as describedabove.

The C₂₋₁₂ alkyl group may be C₃₋₁₂ alkyl, C₄₋₁₂ alkyl, C₅₋₁₂ alkyl orC₆₋₁₂ alkyl.

In one embodiment, —R^(T) is C₀₋₁₂ alkyl(C₃₋₈ cycloalkyl) substituted asdescribed above.

The C₃₋₈ cycloalkyl group may be C₃₋₆ cycloalkyl such as C_(5-6,) forexample C5 cycloalkyl or C₆ cycloalkyl.

In one embodiment —R^(T) bears one substituent.

In one embodiment —R^(T) bears two substituents.

In one embodiment —R^(T) bears three substituents.

In one embodiment —R^(T) bears one, two or three hydroxyl groups, forexample one hydroxyl group.

In one embodiment —R^(T) bears one amine group, for example a C₂₋₁₂alkyl bearing one amine, such as C₂₋₄ alkyl bearing one amine.

In one embodiment —R^(T) bears one, two or three hydroxyl groups, suchas one hydroxyl.

In one embodiment —R^(T) bears one amine group and one hydroxyl group.

In one embodiment —R^(T) bears one amine group and two hydroxyl groups.

In one embodiment wherein —R^(T) bears one or more hydroxyls then thealkyl chain is C₅₋₁₂.

In one embodiment —R^(T) does not bear more than one amine group.

In one embodiment wherein —R^(T) bears more than one substituent, thesubstituents are not located on the same carbon atom.

In one embodiment at least one —R^(T) substituent (such as onesubstituent) is on a terminal carbon of a straight alkyl chain or analkyl branch, for example a straight alkyl chain. Terminal carbon asemployed herein is intended to refer to carbon that would be —CH₃ if itbore no substituents.

In one embodiment, the group —R^(T) is not a group as described above.

—R^(A) and —R^(B)

In one embodiment, —R^(A) is hydrogen.

In one embodiment, —R^(A) is C₁₋₄ alkyl, such as methyl, ethyl orpropyl, such as methyl.

In one embodiment, —R^(B) is hydrogen.

In one embodiment, —R^(B) is C₁₋₄ alkyl, such as methyl, ethyl orpropyl, such as methyl.

In one embodiment, —R^(A) is not ethyl when —R^(B) is hydrogen, methylor ethyl.

In one embodiment, —R^(A) is not methyl when —R^(B) is hydrogen, methylor ethyl.

In one embodiment, —R^(A) is hydrogen and —R^(B) is hydrogen.

In one embodiment, —NR^(A)R^(B) is not a guanidine group.

Terminal Groups of PCT/GB2014/051547 (WO 2014/188178)

The inventors have established that additional compounds having modifiedterminal groups may have biological activity. These additional compoundsare described in PCT/GB2014/051547 (now published as WO 2014/188178).There terminal groups are not described in WO 2013/072695.

The terminal group —R^(T) in the present case may be a group —R⁵ asdescribed in PCT/GB2014/051547 for the compounds of formula (IIa),(IIb), (IIc), (IId), (IIe), (IIf) and (IIg).

Thus, in one embodiment, —R^(T) is a group G-L²-L¹-, and —G is C₅₋₁₂aryl,

-   -   —L¹— is a covalent bond, C₁₋₁₂ alkylene or C₂₋₁₂ heteroalkylene,    -   —L²— is a covalent bond or C₄₋₁₀ heterocyclylene,    -   —R^(T) is substituted with:    -   (i) one, two or three hydroxyl groups, or    -   (ii) one, two or three groups —NR^(A)R^(B), or    -   (iii) one or two groups —NR^(A)R^(B), and one, two or three        hydroxyl groups,

with the proviso that (i), (ii) and (iii) are optional substituents when—L¹— is a nitrogen-containing C₂₋₁₂ heteroalkylene and/or —L²— is anitrogen-containing C₄₋₁₀ heterocyclylene,

-   -   and the aryl group is optionally substituted.

In one embodiment, —R^(T) is a group G-L²-L¹-, and —G is C₃₋₁₀cycloalkyl,

-   -   —L¹— is a covalent bond, C₁₋₁₂ alkylene or C₂₋₁₀ heteroalkylene,    -   —L²— is a covalent bond or C₄₋₁₂ heterocyclylene,    -   with the proviso that —L²— is a covalent bond only when —L¹— is        C₂₋₁₀ heteroalkylene,    -   —R^(T) is substituted with:    -   (i) one, two or three hydroxyl groups, or    -   (ii) one, two or three groups —NR^(A)R^(B), or    -   (iii) one or two groups —NR^(A)R^(B), and one, two or three        hydroxyl groups, with the proviso that (i), (ii) and (iii) are        optional substituents when —L¹— is a nitrogen-containing C₂₋₁₂        heteroalkylene and/or —L²— is a nitrogen-containing C₄₋₁₀        heterocyclylene,    -   and optionally the cycloalkyl group is independently optionally        substituted.

In one embodiment, —R^(T) is G-L²-L¹—, where —G is C₃₋₁₀ cycloalkyl orC₂₋₁₂ alkyl,

-   -   —L¹— is a covalent bond or C₁₋₁₂ alkylene,    -   —L²— is a covalent bond,

with the proviso that —L¹— is not C₁₋₁₂ alkylene when —G is C₂₋₁₂ alkyl,

-   -   —R^(T) is substituted with:    -   (i) two or three groups —NR^(A)R^(B), or    -   (ii) two groups —NR^(A)R^(B), and one, two or three hydroxyl        groups;    -   and the alkyl or cycloalkyl group is independently optionally        substituted.

In one embodiment, —R^(T) is D-L¹—, where D-L¹— is substituted with:

-   -   (i) one, two or three hydroxyl groups, or    -   (ii) one, two or three groups —NR^(A)R^(B), or    -   (iii) one or two groups —NR^(A)R^(B), and one, two or three        hydroxyl groups;    -   —D is C₄₋₁₀ heterocyclyl;    -   —L¹— is a covalent bond, C₁₋₁₂ alkylene or C₂₋₁₂ heteroalkylene,

with the proviso that (i), (ii) and (iii) are optional substituents when—L¹— is a nitrogen-containing C₂₋₁₂ heteroalkylene,

and the heterocyclyl group is independently optionally substituted.

In one embodiment, where -A¹-, -A²- and -A³- are present, —R^(T) is—R^(P).

In one embodiment, where -A¹- is absent, and -A²- and -A³- are present,—R^(T) is —R^(P), with the proviso —X— and —R^(T) together are not anL-α-amino acid residue, such as —X— and —R^(T) together are not L-Lys,L-Arg, L-Dap, L-Ser, L-Dab, L-Dgp (L-α,β-diguanidinopropanoyl) or L-Abu.

The group —R^(P) is as described below.

Where an aryl group is present in —R^(T) it is independently optionallysubstituted one or more substituents selected from —C₁₋₁₀ alkyl, such as—C₁₋₄ alkyl, halo, —CN, —NO₂, —CF_(3,) —NR¹⁰C(O)R¹⁰, —OCF₃, —CON(R¹⁰)₂,—COOR⁹, —OCOR¹⁰, —NR¹⁰COOR¹⁰, —OCON(R¹⁰)₂, —NR¹⁰CON(R¹⁰)_(2,) —OR⁹,—SR⁹, —NR¹⁰SO₂R¹⁰, —SO₂N(R¹⁰)2 and —SO₂R¹⁰ where each —R⁹ isindependently —C₁₋₁₀ alkyl, such as —C₁₋₄ alkyl and each —R¹⁰ isindependently —H or —C₁₋₁₀ alkyl, such as —C₁₋₄ alkyl.

Where an alkyl, cycloalkyl, or heterocyclyl group is present in —R^(T)it is independently optionally substituted one or more substituentsselected from —C₁₋₁₀ alkyl, such as —C₁₋₄ alkyl, halo, —CN, —NO₂, —CF₃,—C(O)R¹⁰, —NR¹⁰C(O)R¹⁰, —OCF₃, —CON(R¹⁰)₂, —COOR⁹, —OCOR¹⁰, —NR¹⁰COOR¹⁰,—OCON(R¹⁰)₂, —NR¹⁰CON(R¹⁰)₂, —OR⁹, —SR⁹, —NR¹⁰SO₂R¹⁰, —SO₂N(R¹⁰)₂ and—SO₂R¹⁰ where each —R⁹ is independently —C₁₋₁₀ alkyl, such as —C₁₋₄alkyl and each —R¹⁰ is independently —H or —C₁₋₁₀ alkyl, such as —C₁₋₄alkyl, except that alkyl is not substituted with alkyl.

—R^(P)

The group —R^(P) is G-L²-L¹—, where

-   -   —G is selected from:        -   C₂₋₁₂ alkyl,        -   C₅₋₁₂ aryl,        -   C₃₋₁₀ cycloalkyl,    -   —L¹— is a covalent bond, C₁₋₁₂ alkylene or C₂₋₁₂ heteroalkylene,    -   —L²— is a covalent bond or C₄₋₁₀ heterocyclylene,    -   with the proviso that —L¹— is not C₁₋₁₂ alkylene when —G is        C₂₋₁₂ alkyl, and G-L²-L¹— is substituted with:    -   (i) one, two or three hydroxyl groups, or    -   (ii) one, two or three groups —NR^(A)R^(B), or    -   (iii) one or two groups —NR^(A)R^(B), and one, two or three        hydroxyl groups, with the proviso that (i), (ii) and (iii) are        optional substituents when —L¹— is a nitrogen-containing C₂₋₁₂        heteroalkylene and/or —L²— is a nitrogen-containing C₄₋₁₀        heterocyclylene,

or —R^(P) is D-L¹—, where —D is C₄₋₁₀ heterocyclyl and —L¹— is asdefined above, and D-L¹— is substituted with:

-   -   (i) one, two or three hydroxyl groups, or    -   (ii) one, two or three groups —NR^(A)R^(B), or    -   (iii) one or two groups —NR^(A)R^(B), and one, two or three        hydroxyl groups,    -   with the proviso that (i), (ii) and (iii) are optional        substituents when —L¹— is a nitrogen-containing C₂₋₁₂        heteroalkylene and/or —D is a nitrogen-containing C₄₋₁₀        heterocyclyl.

The optional substituents may be optional substituents as describedabove.

In one embodiment, —X— and —R^(P) together are not an L-α-amino acid,such as Lys, Arg, Dap, Ser, Phe, Trp, Leu, Ala, α,γ-diaminobutyric acid(Dab) or α,β-diaminopropionic acid (Dap), optionally together with Dgpand Abu.

Terminal Groups of GB 1404301.2 and WO 2015/135976

In the polymyxins, the amino acid residue at position 1 is a diaminobutyric acid (Dab) residue which is acylated at its N-terminal with afatty acyl chain. Within the compounds described in GB 1404301.2, theN-terminal group of Polymyxin comprising Dab and the fatty acyl chain isreplaced by an amine-containing moiety which is linked to a furthersubstituent, but not linked via an amide bond. WO 2015/135976 claimspriority to GB 1404301.2.

The N terminal groups described in GB 1404301.2 may be used in thepresent case. The terminal group —R^(T) in the present case may be agroup —R¹⁵ as described in GB 1404301.2 for the compounds of formula(III). Additionally or alternatively the N terminal groups described inWO 2015/135976 may be used in the present case. The terminal group—R^(T) in the present case may be a group —R¹⁵ as described in WO2015/135976 for the compounds of formula (III).

GB 1404301.2 and WO 2015/135976 do not explicitly described polymyxincompounds where the amino acids at positions 6 and/or 7 are substitutedwith another amino acid.

Previously, it has been thought that the presence of the Dab amino acidresidue at position 1 of Polymyxin B was not important for activity, andthis amino acid could be deleted. Thus, polymyxin nonapeptides are knownin the art for use in the treatment of microorganisms.

The inventors believe that, for optimal activity, an amino substituentis required to mimic the Dab side chain in the naturally-occurringpolymyxin structure. The inventors have therefore described in GB1404301.2 (and also in WO 2015/135976) compounds where an amino group—NR¹⁶R¹⁷ or —N(R¹⁶)— is provided at a carbon atom that is β or γ to agroup —X— at the N-terminal of a polymyxin nonapeptide. The group —X—may be regarded as equivalent to the carbonyl portion —C(O)— of an aminoacid residue at position 1. The inventors have found that compoundswhere an amino group is provided solely at a carbon atom that is a tothe group —X— have inferior biological activity.

Compounds where the amine substituent is provided at a carbon atom thatis β or γ to the group —X— at the N-terminal of PMBN have been describedin WO 2013/072695. However, these compounds, if substituted, have asubstituent on the carbon attached to the amine. The inventors havefound that it is important that a further substituent is provided, andfurthermore that this substituent is not on the carbon attached to theamine. Accordingly the compounds of GB 1404301.2 have an amino group—NR¹⁶R¹⁷ or —N(R¹⁶)— that is connected to a methylene carbon group(—CH₂—).

In some instances, the stereochemistry is an important determinant ofactivity, for example where an additional substituent is provided at thecarbon atom that is a to the group —X—. In these instances, it ispreferred that the stereochemistry at this position is the same as thatof the L-Dab residue in Polymyxin B.

Provided that the amino group remains β- or γ- to the group —X—, theamine group may be part of a nitrogen-containing heterocycle. WO2013/072695 describes compounds having a nitrogen-containing heterocycleat the N terminal of a nonapeptide. However such compounds are notsubstituted. The inventors have found that the addition of a substituentimproves activity. The compounds of GB 1404301.2 (and also WO2015/135976), therefore, where the amine —N(R¹⁶)— is part of a ringstructure, have a ring substituent.

The compounds of GB 1404301.2 are characterised over the polymyxindecapeptides for the reason that the compounds of GB 1404301.2 do notpossess the amide functionality of a polymyxin that is formed from theamino group at the a carbon of the L-Dab group at position 1 and thefatty acyl chain. In the compounds of the present invention, where anamino group is provided at the a carbon, it is not part of an amidegroup. The same comments apply to the compounds of WO 2015/135976.

It is known that polymyxin decapeptides derivatives having a short acylchain (e.g. butanoyl) connected to the L-Dab residue at position 1 viaan amide bond have poor antibacterial activity. For instance thepentanoyl and butanoyl derivatives are reported to be 10-20 times lessactive than Polymyxin B (see de Visser et al. J. Pept. Res. 2003, 61,298).

As noted above, the presence of an amino group solely at the a carbon isnot sufficient to provide good activity. An amino group at a γ or γcarbon is required. Where an amino group, such as —NR¹⁶R¹⁷ or —N(R¹⁶)—is provided at the β or γ carbon, a further substituted amino group maybe provided at the α carbon (this amino group is not part of an amidebond). Such compounds have good activity.

The compounds described in GB 1404301.2 (and also WO 2015/135976) arecompounds corresponding to those of the present case where -A¹- isabsent, -A²- is an L-threonine or L-serine residue and -A³- is an aminoacid residue represented by:

where the asterisk is the point of attachment to -A²- and —R³ is C₁₋₆alkyl, having one amino or one hydroxyl substituent.

Where -A¹-, -A²- and -A³- have these meanings, the group —R^(T) may anamino-containing group —R¹⁵.

In one embodiment, —R^(T) is an amino-containing group:

where:

-   -   —R^(A) is hydrogen or —L^(A)-R^(AA);    -   -Q- is a covalent bond or —CH(R^(B))—;    -   —R^(B) is hydrogen or —L^(B)-R^(BB);    -   or, where -Q- is —CH(R^(B))—, —R^(A) and —R^(B) together form a        5- to 10-membered monocyclic or bicyclic carbocycle, or —R^(A)        and —R^(B) together form a 5- to 10-monocyclic or bicyclic        heterocycle;    -   and, where -Q- is a covalent bond, —R^(A) is —L^(A)—R^(AA), and        where -Q- is —CH(R^(B))— one or both of —R^(A) and —R^(B) is not        hydrogen;    -   —R¹⁶ is independently hydrogen or C₁₋₄ alkyl;    -   —R¹⁷ is independently hydrogen or C₁₋₄ alkyl;    -   or —NR¹⁶R¹⁷ is a guanidine group;    -   or —R¹⁷ and —R^(A) together form a 5- to 10-membered        nitrogen-containing monocyclic or bicyclic heterocycle;    -   or, where -Q- is —CH(R^(B))—, —R¹⁷ and —R^(B) together form a 5-        to 10-membered nitrogen-containing monocyclic or bicyclic        heterocycle;    -   and where —R¹⁷ and —R^(A) together form a monocyclic        nitrogen-containing heterocycle, each ring carbon atom in —R¹⁷        and —R^(A) is optionally mono- or di-substituted with —R^(C),        and the monocyclic heterocycle is substituted with at least one        group selected from —R^(C), —R^(N), —R^(NA) and —L^(B)-R^(BB),        where present,

and where —R¹⁷ and —R^(B) together form a monocyclic nitrogen-containingheterocycle, each ring carbon atom in —R¹⁷ and —R^(B) is optionallymono- or di-substituted with —R^(C), and the monocyclic heterocycle issubstituted with at least one group selected from —R^(C), and —R^(N),where present, or the monocyclic heterocycle is optionally substitutedwhen —R^(A) is —L^(A)—R^(AA),

and a monocyclic nitrogen-containing heterocycle optionally contains onefurther nitrogen, oxygen or sulfur ring atom, and where a furthernitrogen ring atom is present it is optionally substituted with —R^(N),with the exception of a further nitrogen ring atom that is connected tothe carbon that is a to the group —X—, which nitrogen ring atom isoptionally substituted with —R^(NA);

where —R¹⁷ and —R^(A) or —R¹⁷ and —R^(B) together form a bicyclicnitrogen-containing heterocycle, each ring carbon atom in —R¹⁷ and—R^(A) or —R¹⁷ and —R^(B) is optionally mono- or di-substituted with—R^(D);

and the bicyclic nitrogen-containing ring atom heterocycle optionallycontains one, two or three further heteroatoms, where each heteroatom isindependently selected from the group consisting of nitrogen, oxygen andsulfur, and where further nitrogen ring atoms are present, each furthernitrogen ring atom is optionally substituted with —R^(N), with theexception of a nitrogen ring atom that is connected to the carbon thatis a to the group —X—, which nitrogen ring atom is optionallysubstituted with —R^(NA);

where —R^(A) and —R^(B) together form a 5- to 10-membered monocycliccarbocycle or heterocycle, each ring carbon atom in —R^(A) and —R^(B) isoptionally mono- or di-substituted with —R^(C), and a nitrogen ringatom, where present in the monocyclic heterocycle, is optionallysubstituted with —R^(N), with the exception of a nitrogen ring atom thatis connected to the carbon that is α to the group —X—, which nitrogenring atom is optionally substituted with —R^(NA);

where —R^(A) and —R^(B) together form a 5- to 10-membered bicycliccarbocycle or heterocycle, each ring carbon atom in —R^(A) and —R^(B) isoptionally mono- or di-substituted with —R^(D), and a nitrogen ringatom, where present in the bicyclic heterocycle, is optionallysubstituted with —R^(N), with the exception of a nitrogen ring atom thatis

-   -   connected to the carbon that is a to the group —X—, which        nitrogen ring atom is optionally substituted with —R^(NA);    -   and where R¹⁷ and —R^(A) or —R¹⁷ and —R^(B) together form a 5-        to 10-membered nitrogen-containing monocyclic or bicyclic        heterocycle, or where —R^(A) and —R^(B) together form a 5- to        10-membered monocyclic or bicyclic carbocycle, or together form        a 5- to 10-membered monocyclic or bicyclic heterocycle, a carbon        ring atom in —R¹⁷ and —R^(A), —R¹⁷ and —R^(B), or —R^(A) and        —R^(B) is optionally alternatively substituted with oxo (═O);    -   each —R^(C) is independently -L^(C)—R^(CC);    -   each —R^(C) is independently selected from —R^(C), halo, —NO₂,        —OH, and —NH₂,    -   each —R^(N) is independently -L^(N)—R^(NN);    -   each —R^(NA) is independently —R^(L)—R^(NN) or —R^(NN).    -   —R^(AA); —R^(BB); and each —R^(CC) and —R^(NN) where present, is        independently selected from C₁₋₁₂ alkyl, C₃₋₁₀ cycloalkyl, C₄₋₁₀        heterocyclyl, and C₅₋₁₂ aryl;    -   each —L^(A)— is independently a covalent bond or a linking group        selected from —R^(L)—*, —O—L^(AA)-*, —OC(O)—L^(AA)-*,        —N(R¹¹)—L^(AA)-*, and —C(O)—L^(AA)-*, where the asterisk        indicates the point of attachment of the group -L^(A)- to        —R^(AA);    -   each -L^(B)- and -L^(C)- is independently a covalent bond or a        linking group selected from —R^(L)-*, —OC(O)—L^(AA)-*,        —N(R¹¹)—L^(AA)-*, —N(R¹¹)C(O)—L^(AA)-*, —C(O)—L^(AA)-*,        —C(O)O—L^(AA)-*, and —C(O)N(^(R11))-L^(AA)-*, and optionally        further selected from —N(R¹¹)S(O)-L^(AA)-*,        —N(R¹¹)S(O)₂-L^(AA)-*, —S(O)N(R¹¹)-L^(AA)-*, and        —S(O)₂N(R¹¹)-L^(AA)-* where the asterisk indicates the point of        attachment of the group -L^(B)- to —R^(BB) or the group -L^(C)-        to —R^(CC);

each -L^(N)- is independently a covalent bond or a group selected from—S(O)-L^(AA)-*, —S(O)₂-L^(AA)-*, —C(O)-L^(AA)-* and—C(O)N(R¹¹)-L^(AA)-*, where the asterisk indicates the point ofattachment of the group -L^(N)- to —R^(NN);

and each -L^(AA)- is independently a covalent bond or —R^(L)—;

and each —R^(L)— is independently selected from C₁₋₁₂ alkylene, C₂₋₁₂heteroalkylene, C₃₋₁₀ cycloalkylene and C₅₋₁₀ heterocyclylene, and where-L^(AA)- is connected to a group C₁₋₁₂ alkyl, —R^(L)— is not C₁₋₁₂alkylene;

and each C₁₋₁₂ alkyl, C₃₋₁₀ cycloalkyl, C₄₋₁₀ heterocyclyl, C₅₋₁₂ aryl,C₁₋₁₂ alkylene, C₂₋₁₂ heteroalkylene, C₃₋₁₀ cycloalkylene and C₅₋₁₀heterocyclylene group is optionally substituted, where —R^(S) is anoptional substituent to carbon and —R¹² is an optional substituent tonitrogen;

each —R^(S) is independently selected from —OH, —OR¹², —OC(O)R¹², halo,—R¹², —NHR¹², —NR¹²R¹³, —NHC(O)R¹², —N(R¹²)C(O)R¹², —SH, —SR¹²,—C(O)R¹², —C(O)OH, —C(O)OR¹², —C(O)NH₂, —C(O)NHR¹² and C(O)NR¹²R^(13;)except that —R¹² is not a substituent to a C₁₋₁₂ alkyl group; or where acarbon atom is di-substituted with —R^(S), these groups may togetherwith the carbon to which they are attached form a C₃₋₆ carbocycle or aC₅₋₆ heterocycle, where the carbocycle and the heterocycle areoptionally substituted with one or more groups —R¹²;

-   -   each —R¹² is independently C₁₋₆ alkyl, C₁₋₆ haloalkyl, phenyl or        benzyl;    -   each —R¹³ is independently C₁₋₆ alkyl, C₁₋₆ haloalkyl, phenyl or        benzyl;    -   or —R¹² and —R¹³, where attached to N, may together form a 5- or        6-membered heterocyclic ring, which is optionally substituted        with C₁₋₆ alkyl, C₁₋₆ haloalkyl, phenyl or benzyl;

each —R¹¹ is independently hydrogen or C₁₋₄ alkyl.

Polymyxin Compounds of Formula (II)

The compounds of formula (II) are variants of Polymyxin B. The core ofthe compound of formula (II) is a variant of a polymyxin compound, suchas a variant of the polymyxin B decapeptide, nonapeptide (PMBN,Polymyxin 2-10), octapeptide or heptapetide, where the amino acid atposition 6 is substituted with another amino acid as described herein,and optionally the amino acid residues at positions 1, 2, 3, 7 and 10are substituted with another amino acid residue. Optionally one, two orthree of the amino acid residues at positions 1, 2, 3 may be deleted.

The N terminal group of the compounds of formula (II), the group -T^(A),is not particularly limited, but certain preferences are discussedbelow.

The compounds of formula (II) may have the same N terminal groups as thecompounds of formula (I). Where this is the case, the compounds offormula (II) are a selection from the compounds of formula (I). Thus,the group -T^(A) may be a group R^(T)—X— according to the compounds offormula (I).

The compounds of formula (I) and (II) allow for substitution of theamino acid reside at position 6. The substitutions described for thecompounds of formula (II) are a selection of the possible substitutionsdescribed for the compounds of formula (I). The amino acid residues at6-postion in the compounds of formula (II) are believed to be newlydisclosed herein. Thus, the amino acid residue at position 6 is notbelieved to be described in Velkov et al., WO 2010/130007 or WO2012/051663.

Velkov et al. describe substitutions at the 6-position of Polymyxin Band colistin. The authors disclose the replacement of D-phenylalanine orD-leucine at position 6 with three different amino acid residues. Eachamino acid differs from phenylalanine and leucine in the nature of theamino acid side group. Thus, the phenyl group of phenylalanine or thebutyl group of leucine is replaced with octyl (D-OctGly), diphenylmethyl(D-BipAla) or benzyl-protected 4-hydroxyphenyl (D-Tyr(Bzl). No othermodifications to the 6-position are described or suggested.

Velkov et al. also describe the modification of the polymyxin N terminalgroup along with the 6-postion substitution. Thus, the methyloctanoyl ormethylheptanoyl terminal group of Polymyxin B is replaced with octanoyl,biphenylacyl, or phenacyl.

The supplementary information accompanying Velkov et al. shows thatcompounds carrying a D-OctGly, D-BipAla or a D-Tyr(Bzl) substitution atthe 6-position have activity against P. aeruginosa, A. baumannii and K.pneumoniae strains, with MIC values in the range 2-32 mg/L. The variantsare also said to have activity against polymyxin-resistant strains of P.aeruginosa, A. baumannii and K. pneumoniae amongst others.

WO 2010/130007 broadly describes substitutions at the 6- and 7-positionsof polymyxin. The worked examples however only demonstrate thepreparation of compounds that are substituted at the 7-position. All theworked examples retain D-phenylalanine at position 6. The polymyxin Nterminal group is also modified. The worked examples have an octanoyl,nonanoyl or biphenylacyl group at the N terminal.

WO 2012/051663 broadly describes substitutions at the 6- and 7-positionsof polymyxin. The worked examples include compounds where the 6-positionis substituted. However, the examples are limited. In one example, theamino acid residue at position 6 is D-OctGly and in another example theamino acid residue at position 6 is D-Cys(S-Hex) (i.e. a cysteine aminoacid where the thiol group is a hexylthio group). The polymyxin Nterminal group is also modified. The worked examples have an octanoyl,decanoyl, biphenylacyl or biphenylmethylacyl group at the N terminal.

The inventors have found that certain alternative substitutions at the6-postion provide compounds having antimicrobial activity, for exampleagainst Gram-negative bacteria, such as against E. coli, P. aeruginosa,K. pneumonia, and A. Baumannii.

Such substitutions may also enhance antimicrobial activity compared withthe parent unmodified compounds. As shown in the present case, compound2 is a Polymyxin B variant, where the phenylalanine amino acid residueat position 6 is replaced with a phenylalanine analogue bearing a bromosubstituent at the 4-position of the phenyl group. Compound 2 hassuperior activity to Polymyxin B against many E. coli, P. aeruginosa, K.pneumonia, and A. Baumannii strains.

The compounds of formula (II) encompass compounds having amio acidresidues at position 6 that are stucturally non-obvious in the light ofearlier work by Velkov et al.

The present invention provides a compound of formula (II) and the use ofthis compound in a method of treatment. The compound of formula (II) isrepresented thus:

wherein:

-T^(A) is hydrogen, C₁₋₄ alkyl or R^(N)—X—;

-A¹- is absent or is an amino acid residue;

-A²- is absent or is an amino acid residue;

-A³- is absent or is an amino acid residue;

—X— is —C(O)—, —NHC(O)—, —OC(O)—, —CH₂— or —SO₂—;

—R^(N) is a terminal group, such as a group —R^(T) as described herein;

—R^(6A) is C₁₋₁₂ alkyl, C₀₋₁₂ alkyl (C₃₋₁₀ cycloalkyl), C₀₋₁₂ alkyl(C₃₋₁₀ heterocyclyl) or C₀₋₁₂ alkyl (C₅₋₁₀ aryl), where the C₁₋₁₂ alkyl,C₃₋₁₀ cycloalkyl group C₃₋₁₀ heterocyclyl group, and the C₅₋₁₀ arylgroup are optionally substituted, and the optional substituents are asdescribed herein, and with the proviso that —R^(6A) is not benzyl,iso-butyl, iso-propyl, and optionally —R^(6A) is not methyl, phenyl,4-hydroxyphenyl, (1H-indol-3-yl) methyl, 4-phenylphen-1-yl methyl,—(CH₂)₇CH₃, 4-(OBn)-phen-1-yl methyl or —CH₂S(CH₂)₅CH_(3,) andoptionally —R^(6A) is not n-propyl, n-butyl, or tert-butyl;

—R^(7A) together with the carbonyl group and nitrogen alpha to thecarbon to which it is attached is an amino acid residue;

R¹⁰ together with the carbonyl group and nitrogen alpha to the carbon towhich it is attached, is a threonine or leucine residue;

and salts, solvates, protected forms and/or prodrug forms thereof.

It is noted that compounds of formula (II) where —T^(A) is hydrogen (—H)may be used as intermediates for the preparation of compounds of formula(I) and other compounds of formula (II), where —T^(A) is C₁₋₄ alkyl orR^(N)—X—.

In one embodiment, the compound of formula (II) is represented thus:

—R^(6A)

In one embodiment, —R^(6A) is C₁₋₁₂ alkyl, C₀₋₁₂ alkyl(C₃₋₁₀cycloalkyl), C₀₋₁₂ alkyl(C₃₋₁₀ heterocyclyl) or C₀₋₁₂ alkyl(C₅₋₁₀ aryl),where the C₁₋₁₂ alkyl, C₃₋₁₀ cycloalkyl group C₃₋₁₀ heterocyclyl group,and the C₅₋₁₀ aryl group are optionally substituted.

In one embodiment, —R^(6A) is C₀₋₁₂ alkyl(C₃₋₁₀ cycloalkyl), C₀₋₁₂alkyl(C₃₋₁₀ heterocyclyl) or C₀₋₁₂ alkyl(C₅₋₁₀ aryl), where the C₃₋₁₀cycloalkyl group, C₃₋₁₀ heterocyclyl group, and the C₅₋₁₀ aryl group areoptionally substituted.

In one embodiment, —R^(6A) is C₀₋₁₂ alkyl(C₃₋₁₀ cycloalkyl) or C₀₋₁₂alkyl(C₅₋₁₀ aryl), where the C₃₋₁₀ cycloalkyl group and the C₅₋₁₀ arylgroup are optionally substituted.

In one embodiment, the group —R^(6A) is not benzyl, iso-butyl oriso-propyl (the residue at position 6 may not be phenylalanine, leucineor valine, and particularly the D-forms thereof).

additionally or alternatively, in one embodiment the group —R^(6A) isnot methyl, 4-hydroxyphenyl, (1 H-indol-3-yl) methyl or phenyl (theresidue at position 6 may not be alanine, tyrosine, tryptophan andphenylglycine).

In one embodiment, the group —R^(6A) is not 4-phenylphen-1-yl methyl,—(CH₂)₇CH₃, 4-(OBn)-phen-1-yl or —CH₂S(CH₂)₅CH₃.

Additionally or alternatively, the residue at position 6 may not benorvaline, norleucine and t-butylglycine, particularly the D-formsthereof. Thus, the group —R^(6A) may not be n-propyl, n-butyl andtert-butyl.

Alternatively, the residue at position 6 may not be phenylalanine,leucine, norvaline, norleucine and t-butylglycine, particularly theD-forms thereof. Thus, the group —R^(6A) may not be benzyl, iso-butyl,n-propyl, n-butyl and tert-butyl.

The C₁₋₁₂ alkyl group, C₃₋₁₀ cycloalkyl group, C₃₋₁₀ heterocyclyl group,and the C₅₋₁₀ aryl group may be substituted, such as optionallysubstituted with one or more groups —R^(Z), where each group —R^(Z) isselected from halo, optionally substituted C₁₋₁₂ alkyl, optionallysubstituted C₂₋₁₂ alkenyl, optionally substituted C₂₋₁₂ alkynyl,optionally substituted C₃₋₁₀ cycloalkyl, optionally substituted C₃₋₁₀heterocyclyl, optionally substituted C₅₋₁₂ aryl, —CN, —NO₂, —OR^(Q),—SR^(Q), —N(R^(W))C(O)R^(Q), —N(R^(Q))₂, and —C(O)N(R^(Q))₂,

-   -   where —R^(W) is H or C₁₋₄ alkyl; and    -   —R^(Q) is H or —R^(Q1), and —R^(Q1) is selected from optionally        substituted C₁₋₁₂ alkyl, C₂₋₁₂ alkenyl, C₂₋₁₂ alkynyl, and C₅₋₁₂        aryl,

and in a group —N(R^(Q))₂ the groups —R^(Q) may together with thenitrogen atom to which they are attached form a C₅₋₆ heterocycle, wherethe heterocycle is optionally substituted,

-   -   with the proviso that C₁₋₁₂ alkyl is not substituted with alkyl,        alkenyl or alkynyl.

The group —R^(6A) together with the carbonyl group and nitrogen alpha tothe carbon to which it is attached is not a leucine, iso-leucine,phenylalanine, threonine, valine or nor-valine residue. Additionally oralternatively, —R^(6A) together with the carbonyl group and nitrogenalpha to the carbon to which it is attached is not a tyrosine residue.

As noted above, the C₁₋₁₂ alkyl group, C₃₋₁₀ cycloalkyl group, C₃₋₁₀heterocyclyl group, and the C₅₋₁₀ aryl group may be substituted with oneor more groups —R^(Z). Examples of —R^(Z) include optionally substitutedalkyl, alkenyl, alkynyl, cycloalkyl, aryl and heterocycle groups.

Where a group, such as alkyl, alkenyl, alkynyl, cycloalkyl, aryl andheterocycle, is optionally substituted, the group may have one or moresubstituent groups selected from halo, haloalkyl, alkyl, alkenyl,alkynyl, and aryl, except that alkyl alkenyl, and alkynyl groups are notsubstituents to the alkyl alkenyl, and alkynyl groups. Suitable groupsare described in relation to the definition of —R^(P) for —R⁶.

In one embodiment, —R^(6A) is C₀₋₁₂ alkyl(C₅₋₁₀ aryl), where the C₅₋₁₀aryl group is optionally substituted, and the C₅₋₁₀ aryl group issubstituted with one or more groups —R^(Z), where each group —R^(Z) isselected from halo, optionally substituted C₁₋₁₂ alkyl, —CN, and —NO₂.

In one embodiment, —R^(6A) is C₀₋₁₂ alkyl(C₅₋₁₀ aryl), where the C₅₋₁₀aryl group is optionally substituted, and the C₅₋₁₀ aryl group issubstituted with one or more groups —R^(Z), where each group —R^(Z) isselected from halo, optionally substituted C₁₋₁₂ alkyl, optionallysubstituted C₂₋₁₂ alkenyl, —CN, and —NO₂.

In one embodiment, —R^(6A) is C₀₋₁₂ alkyl(C₃₋₁₀ cycloalkyl), where theC₃₋₁₀ cycloalkyl group is optionally substituted, and the C₃₋₁₀cycloalkyl group is substituted with one or more groups —R^(Z), whereeach group —R^(Z) is selected from halo, optionally substituted C₁₋₁₂alkyl, optionally substituted C₂₋₁₂ alkenyl, optionally substitutedC₂₋₁₂ alkynyl, optionally substituted C₃₋₁₀ cycloalkyl, optionallysubstituted C₃₋₁₀ heterocyclyl, optionally substituted C₅₋₁₂ aryl,—OR^(Q), —SR^(Q), —N(R^(W))C(O)R^(Q), —N(R^(Q))₂, and —C(O)N(R^(Q))₂.

In one embodiment, —R^(6A) is C₀₋₁₂ alkyl(C₆ cycloalkyl), such as C₁alkyl(C₆ cycloalkyl). The worked examples in the present case includenumerous compounds where the group —R^(6A) is C₁ alkyl(C6 cycloalkyl)(—CH₂(C₆H₁₁)).

In one embodiment, —R^(6A) is optionally substituted C₁₋₁₂ alkyl, wherethe C₁₋₁₂ alkyl is optionally substituted with one or more groupsselected from halo, such as fluoro, optionally substituted C₃₋₁₀cycloalkyl, optionally substituted C₃₋₁₀ heterocyclyl, optionallysubstituted C₅₋₁₂ aryl, —CN, —NO₂, —OR^(Q), —SR^(Q), —N(R^(W))C(O)R^(Q),—N(R^(Q))₂, and —C(O)N(R^(Q))₂.

In one embodiment, —R^(6A) is optionally substituted C₁₋₁₂ alkyl.

The alkyl group is typically a C₁₋₁₂ alkyl group, such as C₂₋₁₂ alkyl,such as C_(s-12) alkyl, such as C₄₋₁₂ alkyl, such as C₅₋₁₂ alkyl, suchas C₆₋₁₂ alkyl, such as C₈₋₁₂ alkyl, for example C₂₋₁₀ alkyl, C₄₋₁₀alkyl, C₅₋₁₀ alkyl and C₆₋₁₀ alkyl.

The alkyl group may be a C₉₋₁₂ alkyl group, such as C₉, C₁₁ and C₁₂alkyl.

The alkyl group may be a C₁₋₅ alkyl group.

The alkyl group may be a C₅₋₁₂ alkyl group.

In one embodiment, —R^(6A) is optionally substituted C₂₋₁₂ alkyl.

The alkyl group may be linear or branched.

Where the alkyl group is substituted, it may be monosubstituted. Asubstituent may be provided at a terminal of the alkyl group.

A C₀₋₁₂ alkyl group may be a C₁₋₁₂ alkyl group, such a C₂₋₁₂ alkylgroup, a C₁₋₃ alkyl group, and a C₅₋₁₂ alkyl group.

In one embodiment, a C₀₋₁₂ alkyl group is C₁ alkyl.

In one embodiment, a C₀₋₁₂ alkyl group is C₀ alkyl.

In one embodiment, a C₀₋₁₂ alkyl group is not linear C₄ alkyl.

In one embodiment, a C₀₋₁₂ alkyl group is not C₀ alkyl and/or C₁ alkyl.

In one embodiment, —R^(6A) is not —CH₂S(CH₂)₅CH₃, —CH₂O(CH₂)₅CH₃,—CH₂S(CH₂)₅CF₃, —CH2OCH2Ph, or —CH₂SCH₂Ph.

In one embodiment, —R^(6A) is C₀₋₁₂ alkyl(C₅₋₁₀ aryl), such as C₁₋₁₂alkyl(C₅₋₁₀ aryl), where the C₅₋₁₀ aryl group is optionally substituted.

In one embodiment, —R^(6A) is C₀₋₁ alkyl(C₅₋₁₀ aryl).

In one embodiment, —R^(6A) is C₂₋₁₂ alkyl(C₅₋₁₀ aryl).

In one embodiment, —R^(6A) is C₀₋₁₂ alkyl(C₅₋₁₀ heteroaryl).

In one embodiment, —R^(6A) is C₀₋₁₂ alkyl(C₅₋₁₀ aryl), where the aryl isoptionally substituted with halo, optionally substituted C₂₋₁₂ alkenyl,optionally substituted C₂₋₁₂ alkynyl, substituted C₃₋₁₀ cycloalkyl,optionally substituted C₃₋₁₀ heterocyclyl, substituted C₅₋₁₂ aryl, —CN,—NO₂, —SR^(Q), —N(R^(W))C(O)R^(Q), —N(R^(Q))₂, and —C(O)N(R^(Q))₂.

In one embodiment, —R^(6A) is C₀₋₁₂ alkyl(C₅₋₁₀ aryl), where the aryl isoptionally substituted with halo, optionally substituted C₂₋₁₂ alkenyl,optionally substituted C₂₋₁₂ alkynyl, optionally substituted C₃₋₁₀heterocyclyl, —CN, —NO₂, —SR^(Q), —N(R^(W))C(O)R^(Q), —N(R^(Q))₂, and—C(O)N(R^(Q))₂.

The aryl group may be a carboaryl or heteroaryl group.

The carboaryl group may be phenyl. The alkyl group may be linear orbranched.

In one embodiment, —R^(6A) is substituted benzyl (—CH₂Ph).

In one embodiment, —R^(6A) is monosubstituted benzyl.

In one embodiment, —R^(6A) is monosubstituted benzyl, where the phenylgroup is substituted at the 2-, 3- or 4-position, such as the 2- or4-position.

In one embodiment, —R^(6A) is monosubstituted benzyl, where the phenylgroup is substituted at the 2-position with halo, optionally substitutedalkyl, optionally substituted alkenyl, optionally substitutedcycloalkyl, or optionally substituted aryl.

In one embodiment, —R^(6A) is monosubstituted benzyl, where the phenylgroup is substituted at the 2-position with halo, optionally substitutedalkyl, optionally substituted cycloalkyl, or optionally substitutedaryl.

In one embodiment, —R^(6A) is monosubstituted benzyl, where the phenylgroup is substituted at the 2-position with halo, optionally substitutedalkyl, or optionally substituted aryl.

In one embodiment, —R^(6A) is monosubstituted benzyl, where the phenylgroup is substituted at the 4-position with halo, optionally substitutedalkyl, optionally substituted alkenyl, optionally substituted aryl oroptionally substituted heteroaryl.

In one embodiment, —R^(6A) is monosubstituted benzyl, where the phenylgroup is substituted at the 4-position with halo, optionally substitutedalkyl, optionally substituted aryl or optionally substituted heteroaryl.

In one embodiment, —R^(6A) is monosubstituted benzyl, where the phenylgroup is substituted at the 4-position with halo, optionally substitutedalkyl, substituted aryl or optionally substituted heteroaryl.

In one embodiment, —R^(6A) is monosubstituted benzyl, where the phenylgroup is substituted at the 3-position with halo, optionally substitutedalkyl, optionally substituted alkenyl, substituted aryl or optionallysubstituted heteroaryl.

In one embodiment, —R^(6A) is monosubstituted benzyl, where the phenylgroup is substituted at the 3-position with halo, optionally substitutedalkyl, substituted aryl or optionally substituted heteroaryl.

In one embodiment, —R^(6A) is monosubstituted benzyl, where the phenylgroup is substituted at the 2-position with aryl, such as phenyl.

In one embodiment, —R^(6A) is monosubstituted benzyl, where the phenylgroup is substituted at the 3-position with aryl, such as C₅₋₁₀ aryl,such as C₅₋₆ aryl, such as phenyl or pyridine. The aryl group isoptionally substituted, such as substituted.

In one embodiment, —R^(6A) is monosubstituted benzyl, where the phenylgroup is substituted at the 4-position with aryl, such as C₅₋₁₀ aryl,such as C₅₋₆ aryl, such as phenyl or pyridine. The aryl group isoptionally substituted, such as substituted.

In one embodiment, —R^(6A) is monosubstituted benzyl, where the phenylgroup is substituted at the 3-position with heteroaryl, such as C₅₋₁₀heteroaryl, such as C₅₋₆ heteroaryl, such as pyridine.

In one embodiment, —R^(6A) is monosubstituted benzyl, where the phenylgroup is substituted at the 4-position with heteroaryl, such as C5-10heteroaryl, such as C₅₋₆ heteroaryl, such as pyridine.

In one embodiment, —R^(6A) is monosubstituted benzyl, where the phenylgroup is substituted at the 3-position with halo, such as bromo.

In one embodiment, —R^(6A) is monosubstituted benzyl, where the phenylgroup is substituted at the 4-position with halo, such as bromo.

In one embodiment, —R^(6A) is monosubstituted benzyl, where the phenylgroup is substituted at the 3-position with alkyl, such as C₁₋₁₂ alkyl,such as C₂₋₁₂ alkyl, such as C₆₋₁₂ alkyl, such as C₈ alkyl. The alkylgroup may be linear or branched.

In one embodiment, —R^(6A) is monosubstituted benzyl, where the phenylgroup is substituted at the 4-position with alkyl, such as C₁₋₁₂ alkyl,such as C₂₋₁₂ alkyl, such as C₆₋₁₂ alkyl, such as C₈ alkyl. The alkylgroup may be linear or branched.

In one embodiment, —R^(6A) is C₀₋₁₂ alkyl(C₃₋₁₀ cycloalkyl), such asC₁₋₁₂ alkyl(C₃₋₁₀ cycloalkyl), where the C₃₋₁₀ cycloalkyl group isoptionally substituted.

In one embodiment, —R^(6A) is C₁ alkyl(C₃₋₁₀ cycloalkyl), such as C₁alkyl(cyclohexyl), where the C₃₋₁₀ cycloalkyl group is optionallysubstituted.

In one embodiment, —R^(6A) is C₁₋₁₂ alkyl(cyclohexyl). Compounds of thistype may be prepared from compounds where —R^(6A) is C₁₋₁₆ alkyl(phenyl)by appropriate reduction of the phenyl group, such as described herein.

In one embodiment, —R^(6A) is C₀₋₁₂ alkyl(C₃₋₁₀ cycloalkyl), such as C₁alkyl(cyclohexyl), where the C₃₋₁₀ cycloalkyl group is optionallysubstituted with one or more groups selected from halo, substitutedC₁₋₁₂ alkyl, optionally substituted C₂₋₁₂ alkenyl, optionallysubstituted C₂₋₁₂ alkynyl, optionally substituted C₃₋₁₀ cycloalkyl,optionally substituted C₃₋₁₀ heterocyclyl, optionally substituted C₅₋₁₂aryl, —CN, —NO₂, —OR^(Q), —SR^(Q), —N(R^(W))C(O)R^(Q), —N(R^(Q))₂, and—C(O)N(R^(Q))₂.

In one embodiment, —R^(6A) is C₀₋₁₂ alkyl(C₃₋₁₀ cycloalkyl), such as C₁alkyl(cyclohexyl), where the C₃₋₁₀ cycloalkyl group is optionallysubstituted with one or more groups selected from halo, optionallysubstituted C₂₋₁₂ alkenyl, optionally substituted C₂₋₁₂ alkynyl,optionally substituted C₃₋₁₀ cycloalkyl, optionally substituted C₃₋₁₀heterocyclyl, optionally substituted C₅₋₁₂ aryl, —CN, —NO₂, —OR^(Q),—SR^(Q), —N(R^(W))C(O)R^(Q), —N(R^(Q))₂, and —C(O)N(R^(Q))₂.

The C₃₋₁₀ cycloalkyl may be a C₅₋₇ cycloalkyl group, such as C₅₋₆cycloalkyl group.

In one embodiment, C₃₋₁₀ cycloalkyl is cyclopentyl or cyclohexyl, suchas cyclohexyl.

A cycloalkyl group may be optionally substituted, such as optionallymonosubstituted.

Where, the cycloalkyl group is cyclohexyl, the cyclohexyl is optionallysubstituted at the 2-, 3- or 4-position, such as the 2- or 4-position,such as the 4-position.

In one embodiment, —R⁶ and/or —R⁷ is not —(CH₂)₄-cyclcohexyl.

In one embodiment, —R⁶ and/or —R⁷ is not —(C₆H₁₀)—Pr, such as where the-Pr group is a linear propyl group.

In one embodiment, —R^(6A) is C₀₋₁₂ alkyl(C₃₋₁₀ heterocyclyl) such asC₁₋₁₂ alkyl(C₃₋₁₀ heterocyclyl), where the C₃₋₁₀ heterocyclyl group isoptionally substituted. Where C₀₋₁₂ alkyl is C₀, the heteroatom of theheterocyclyl group is not provided at the β position (i.e. theheteroatom is not connected to the a carbon).

The heterocyclyl group contains a heteroatom selected from N, O and S,and optionally contains further heteroatoms. A reference to N is areference to a group —NH— within a heterocycle, and a reference to S is—S—, —S(O)— or —S(O)₂—.

The heterocyclyl may be substituted at a carbon ring atom or a nitrogenring atom, if such is present. Where a nitrogen ring atom is substitutedthe substituent may be a group —R^(Z) selected from optionallysubstituted C₁₋₁₂ alkyl, optionally substituted C₂₋₁₂ alkenyl,optionally substituted C₂₋₁₂ alkynyl, optionally substituted C₃₋₁₀cycloalkyl, optionally substituted C₃₋₁₀ heterocyclyl, optionallysubstituted C₅₋₁₂ aryl, and —C(O)N(R^(Q))_(2.) Where a carbon ring atomis substituted the substituent may be a group —R^(Z) such as describedabove.

The heterocyclyl may be C₅₋₁₀, such as C₅₋₆, such as C₅ or C₆heterocyclyl.

The heterocyclyl may be selected from the group consisting ofpiperidinyl, piperazinyl, morpholinyl and thiomorpholinyl.

Where an alkyl group is optionally substituted with halo, it ispreferred that the alkyl group is optionally substituted with fluoro.

In one embodiment, —R^(6A) is not 4-hydroxyphenylmethyl (i.e. —R⁶together with the carbonyl group and nitrogen alpha to the carbon towhich it is attached is not a tyrosine residue).

The comments above refer to compounds where the a amino acid residue atposition 6 has a a carbon atom that is substituted with —R^(6A) and —H.The —H may also be a site for substitution, providing di-substituted aamino acid residues at position 6.

In an alternative embodiment, a carbon atom at within the a amino acidresidue at position 6 is di-substituted, where each substituent is agroup —R^(6A) as described herein.

In an alternative embodiment, the a carbon atom at within the a aminoacid residue at position 6 is di-substituted, where each substituent isa group —R^(6A), where the groups —R^(6A) may together with the α carbonatom to which they are attached form a C₄₋₆ carbocycle or a C₅₋₆heterocycle, wherein the carbocycle and the heterocycle are optionallysubstituted with one or more groups —R^(Z), as described above. Thecarbocycle is a cycloalkyl group as described herein. The heterocycle isa heterocyclyl group as described herein.

Where a heterocycle is present the heteroatom of the heterocyclyl groupis not provided at the β position (i.e. the heteroatom is not connectedto the a carbon).

The heterocycle contains a heteroatom selected from N, O and S, andoptionally contains further heteroatoms. A reference to N is a referenceto a group —NH— within a heterocycle, and a reference to S is —S—,—S(O)— or —S(O)₂—.

The heterocyclyl may be substituted at a carbon ring atom or a nitrogenring atom, if such is present. Where a nitrogen ring atom is substitutedthe substituent may be a group —R^(Z) selected from optionallysubstituted C₁₋₁₂ alkyl, optionally substituted C₂₋₁₂ alkenyl,optionally substituted C₂₋₁₂ alkynyl, optionally substituted C₃₋₁₀cycloalkyl, optionally substituted C₃₋₁₀ heterocyclyl, optionallysubstituted C₅₋₁₂ aryl, and —C(O)N(R^(Q))_(2.) Where a carbon ring atomis substituted the substituent may be a group —R^(Z) such as describedabove.

The heterocycle may be selected from the groups piperidine, piperazine,morpholine and thiomorpholine.

In one embodiment, —R^(6A) together with the carbonyl group and nitrogenalpha to the carbon to which it is attached is an amino having apiperidine side chain that is a gem di-substituent to the α-carbon. Thusthe α-carbon is a ring atom in the piperidine ring. This is a cyclicanalogue of Dab.

In one embodiment, —R^(Z) is selected from halo, optionally substitutedC₁₋₁₂ alkyl, optionally substituted C₂₋₁₂ alkenyl, optionallysubstituted C₂₋₁₂ alkynyl, optionally substituted C₅₋₁₂ aryl, —OR^(Q),—SR^(Q), —N(R^(W))C(O)R^(Q), —N(R^(Q))₂, and —C(O)N(R^(Q))₂.

In one embodiment, —R^(Z) is selected from halo, optionally substitutedC₂₋₁₂ alkenyl, optionally substituted C₂₋₁₂ alkynyl, optionallysubstituted C₃₋₁₀ cycloalkyl, optionally substituted C₅₋₁₂ aryl,—OR^(Q), —SR^(Q), —N(R^(W))C(O)R^(Q), —N(R^(Q))₂, and —C(O)N(R^(Q))₂.

In one embodiment, —R^(Z) is selected from halo, optionally substitutedC₂₋₁₂ alkenyl, optionally substituted C₂₋₁₂ alkynyl, optionallysubstituted C₅₋₁₂ aryl, —OR^(Q), —SR^(Q), —N(R^(W))C(O)R^(Q),—N(R^(Q))₂, and —C(O)N(R^(Q))₂.

In one embodiment, —R^(Z) is selected from halo, optionally substitutedC₁₋₁₂ alkyl, optionally substituted C₂₋₁₂ alkenyl, optionallysubstituted C₂₋₁₂ alkynyl, optionally substituted C₃₋₁₀ cycloalkyl,—OR^(Q), —SR^(Q), —N(R^(W))C(O)R^(Q), —N(R^(Q))₂, and —C(O)N(R^(Q))₂.

In one embodiment, —R^(Z) is selected from halo, optionally substitutedC₂₋₁₂ alkenyl, optionally substituted C₂₋₁₂ alkynyl, —OR^(Q), —SR^(Q),—N(R^(W))C(O)R^(Q), —N(R^(Q))₂, and —C(O)N(R^(Q))₂.

In one embodiment, the amino acid residue at position 6 is an L- orD-amino acid residue, such as a D-amino acid residue.

—R^(7A)

In one embodiment, —R^(7A) together with the carbonyl group and nitrogenalpha to the carbon to which it is attached may be a leucine,iso-leucine, phenylalanine, threonine, valine or nor-valine residue

In one embodiment, the group —R^(7A) may be a group —R⁷ as describedabove for the compounds of formula (I).

In one embodiment, —R^(7A) together with the carbonyl group and nitrogenalpha to the carbon to which it is attached is an amino acid residueselected from the group consisting of leucine, OctGly, BipAla, and Cys,such as Cys(S-Hex) and Cys(S-Bzl), and for example the L-forms thereof.Additionally or alternatively, —R^(7A) together with the carbonyl groupand nitrogen alpha to the carbon to which it is an amino acid residueselected from the group consisting of threonine, serine, valine,2-aminobutyric acid (Abu) and 2-aminoisobutyric acid (Aib), and forexample the L-forms thereof.

In one embodiment, —R^(7A) together with the carbonyl group and nitrogenalpha to the carbon to which it is a leucine residue, such as L-leucine.In this embodiment, the amino acid residue at the 7-position is notsubstituted with reference to the amino acid residue at the 7-positionof Polymyxin B.

In one embodiment, —R^(7A) together with the carbonyl group and nitrogenalpha to the carbon to which it is attached is an amino acid residueselected from the group consisting of leucine, alanine, phenylalanine,OctGly, BipAla, Cys, such as Cys(S-Hex) and Cys(S-Bzl), threonine,serine, valine, 2-aminobutyric acid (Abu) and 2-aminoisobutyric acid(Aib), and for example the L-forms thereof.

In one embodiment, the amino acid residue at position 7 is an L- orD-amino acid residue, such as an L-amino acid residue.

—T^(A)

In one embodiment, —T^(A) is hydrogen or —X—R^(N).

In one embodiment, —T^(A) is hydrogen. Such a compound has a free aminogroup (primary amine, —NH₂) at the N terminal.

In one embodiment, —T^(A) is C₁₋₄ alkyl. Here, the compound has analkylated amino group at the N terminal. The C₁₋₄ alkyl group may belinear or branched. The C₁₋₄ alkyl group may be selected from methyl,ethyl, propyl and butyl, such as methyl and ethyl. The C₁₋₄ alkyl groupmay be methyl.

In one embodiment, —T^(A) is —X—R^(N). Here, the N terminal group of thecompound is modified. Modifications to the N terminal are well known inthe art. Indeed, the natural products

Polymyxin B and Colistin are also modified at the N terminal.

—X—

The group —X— is as defined from the compounds of formula (I).

—R^(N)

The group —R^(N) is a terminal group.

The terminal group may be a group that retains biological activity orprovides improved biological activity when that group is compared withthe terminal group present in Polymyxin B and Colistin.

In one embodiment, the group —R^(N) is a group —R^(T) as defined abovefor the compounds of formula (I). The group —R^(T) typically possesseshydroxyl and/or amino functionality.

Alternatively, the group —R^(N) may be a lipophilic group.

In one embodiment, —R^(N) is benzyl. In one embodiment, —R^(N) isM-L¹¹-L¹⁰-, where:

-   -   -L¹⁰- is a covalent bond, C₁₋₁₂ alkylene or C₂₋₁₂        heteroalkylene,    -   -M is selected from optionally substituted C₁₋₁₂ alkyl, C₂₋₁₂        alkenyl, C₃₋₁₀ cycloalkyl and C₅₋₁₂ aryl,    -   and with the proviso that -L¹⁰- is not C₁₋₁₂ alkylene when -M is        C₁₋₁₂ alkyl.

The optional substituents may be selected from the group consisting ofoptionally substituted C₁₋₁₀ alkyl, C₂₋₁₂ alkenyl, C₅₋₁₂ aryl, C₃₋₁₀cycloalkyl, —OH, —OR¹⁹, —NH₂, —NHR¹⁹, —N(R¹⁹)₂, —COOR¹⁹, —OCOR¹⁹,—CON(R¹⁰)_(2,) and —NR¹⁰C(O)R¹⁰, where each —R¹⁹ is independently C₁₋₁₀alkyl, C₂₋₁₂ alkenyl, C₅₋₁₂ aryl, C₃₋₁₀ cycloalkyl, and the optionalsubstituents are —OH and —NH₂.

In one embodiment, —R^(N) is selected from optionally substituted C₁₋₁₂alkyl and -L¹²-V, where -L¹²- is absent or C₂₋₄ alkenyl, and V— isoptionally substituted C₅₋₁₂ aryl, such as C₆₋₁₀ carboaryl and C₅₋₁₂heteroaryl, where the optional substituent is W-L¹²-, and:

-   -   -L¹³- is a covalent bond, C₁₋₃ alkylene or C₂₋₇ heteroalkylene,    -   —W is C₅₋₁₂ aryl, such as C₆₋₁₀ carboaryl and C₅₋₁₂ heteroaryl.

In one embodiment, —R^(N) is C₁₋₁₂ alkyl.

A C₁₋₁₂ alkyl group may be a C₄₋₁₂, C₆₋₁₂, C₄₋₁₀ or a C₆₋₁₀ alkyl group.

An alkyl group may be linear or branched.

In one embodiment, the alkyl group is C₆₋₈ alkyl. As noted above, analkyl group may be linear or branched. Where the C₆₋₈ alkyl group isbranched, the branch point may be located at the penultimate carbon ofthe longest linear alkyl chain. The branch may be a methyl branch.

In one embodiment, —R^(N) is 5-methylheptyl, for example where —X— is—C(O)—. Such a group is the N terminal group is present in Polymyxin B1and Colistin A (i.e. where —X—R^(N) together are 6-methyloctanoyl).

In one embodiment, —R^(N) is 5-methylhexyl, for example where —X— is—C(O)—. Such a group is the N terminal group is present in Polymyxin B2and Colistin B (i.e. where —X—R^(N) together are 6-methylheptanoyl).

In one embodiment, R^(N) is heptyl, for example where —X— is —C(O)—.Such a group is the N terminal group is present in Polymyxin B3 (i.e.where —X—R^(N) together are 6-octanoyl). In one embodiment, —R^(N) ishexyl, for example where —X— is —C(O)—. Such a group is the N terminalgroup is present in Polymyxin B4 (i.e. where —X—R^(N) together areheptanoyl).

In one embodiment, —R^(N) is diphenylmethyl, such as4-phenylphenylmethyl.

In one embodiment, —R^(N) is optionally substituted C₅₋₁₀ aryl.

In one embodiment, the optionally substituted C₅₋₁₀ aryl is phenylsubstituted with phenyl (i.e. biphenyl), for example 4-phenylphenyl or2-phenylphenyl.

In one embodiment, —R^(N) is phenyl or benzyl, where the phenyl orbenzyl is optionally substituted with one or more halo or nitro groups.

In one embodiment, —R^(N) is halophenyl, such as chlorophenyl, such as2-chlorophenyl for example where —X— is —NH(CO)—.

In one embodiment, —R^(N) together with —X— is not a group R¹ asdescribed in WO 2015/149131, for example where -A¹- is L-Dap, L-Dab orL-Lys, -A² is L-Thr, and -A³- is L-Dap, L-Dab or L-Lys.

-A¹-, -A²- and -A³ -

In one embodiment, -A¹- is absent, and -A²- and -A³- are present.

In one embodiment, -A¹- and -A²- are absent, and -A³- is present. Such acompound may be referred to as an octapeptide.

In one embodiment, -A¹-, -A²- and -A³- are absent. Such a compound maybe referred to as a heptapeptide.

Each of -A¹-, -A²- and -A³- may be an α-amino acid.

A reference to an α-amino acid includes proteinogenic (“natural”)α-amino acids, optionally together with other α-amino acids.

Examples of α-amino acids that are not proteinogenic are those aminoacids generated by post-translational modification, or by other means.Examples include Dab, Dap, Dgp (α,β-diguanidinopropanoyl), ornithine andnor-valine

Also included are amino having a piperidine side chain that is a gemdi-substituent to the α-carbon. Thus the α-carbon is a ring atom in thepiperidine ring. This is a cyclic analogue of Dab.

An amino acid, such as an α-amino acid, may be an L- or D-amino acid. Inone embodiment, each of -A¹-, -A²- and -A³-, where present, is anL-amino acid.

In one embodiment, where one or more of -A¹-, -A²- and -A³- is absent,and optionally where all of -A¹-, -A²- and -A³- are present, R^(T)-X—may be an α-amino acid residue, such as an α-amino acid residue selectedfrom the group consisting of Ala, Ser, Thr, Val, Leu, Ile, Pro, Phe,Tyr, Trp, His, Lys, Arg, α,γ-diaminobutyric acid (Dab) andα,β-diaminopropionic acid (Dap).

In one embodiment, -A³- is an amino acid residue represented by:

-   -   where the asterisk is the point of attachment to -A²-, and —R³        corresponds to the side chain of an amino acid at position 3 in        the polymyxin compounds.

In one embodiment, the group —R³ together the carbonyl group andnitrogen alpha to the carbon to which it is attached, is an amino acidresidue having an amino- and/or hydroxyl-containing side chain. Thus,the group —R³ has amino and/or hydroxyl functionality.

In one embodiment, for the compounds of formula (II) each of -A¹-, -A²-and -A³- has the same meaning as the compounds of formula (I).

Protected Forms

Compounds of the invention, such as compounds of formula (I) and (II),may be provided in a protected form. Here, reactive functionality, suchas amino functionality, may be masked in order to prevent its reactionduring a synthesis step. A protecting group is provided to mask thereactive functionality, and this protecting groups may be removed at alater stage of the synthesis to reveal the original reactivefunctionality.

A compound of formula (Ia) is provided, and salts, solvates and hydratesthereof, which is a compound of formula (I) in protected form. Forexample, amino, hydroxyl, carboxyl and thiol functionality present incompound (I) may be protected with a protecting group, such as describedherein. The compound of formula (Ia) may be an intermediate for thepreparation of the compound of formula (I). Thus, compound (I) may beprepared from compound (la), for example by removal of the protectinggroups (“deprotection”).

Similarly, a compound of formula (IIa) is provided, and salts, solvatesand hydrates thereof, which is a compound of formula (II) in protectedform. For example, amino, hydroxyl, carboxyl and thiol functionalitypresent in compound (II) may be protected with a protecting group, suchas described herein. The compound of formula (IIa) may be anintermediate for the preparation of the compound of formula (II). Thus,compound (II) may be prepared from compound (IIa), for example byremoval of the protecting groups (“deprotection”).

In one embodiment, the protected form is a compound where amino,hydroxyl, thiol, and/or carboxyl functionality is protected (masked) bya protecting group. In one embodiment, the protected form is a compoundwhere the side chain functionality of the amino acids residues with thecompound are protected.

In the compound of formula (I) and (II), the amino acid residues atpositions 5, 8 and 9 are Dab residues, and the side chain of the Dabresidue includes amino functionality. The amino acid functionality ofeach Dab residue may be protected with an amino protecting group, asdescribed herein.

In certain embodiments of the invention, amino acid residue -A³-, wherepresent, is an amino acid residue where the side chain includes aminofunctionality. Examples of -A³- include Dab, a lysine residue, anornithine residue, and Dap residues. The amino functionality of theseresidues may be protected with an amino protecting group, as describedherein.

In certain embodiments of the invention, amino acid residue -A³-, wherepresent, is an amino acid residue where the side chain includes hydroxylfunctionality. Examples of -A³- include serine and threonine residues.The hydroxyl functionality of these residues may be protected with anhydroxyl protecting group, as described herein.

In certain embodiments of the invention, amino acid residue -A²-, wherepresent, is an amino acid residue where the side chain includes hydroxylfunctionality. Examples of -A²- include serine and threonine residues.The hydroxyl functionality of these residues may be protected with anhydroxyl protecting group, as described herein. In certain embodimentsof the invention, amino acid residue -A²-, where present, is an aminoacid residue where the side chain includes amino functionality. Theamino functionality of these residues may be protected with an hydroxylprotecting group, as described herein.

In certain embodiments of the invention, amino acid residue -A¹-, wherepresent, is an amino acid residue where the side chain includes amino orhydroxyl functionality. Examples include those amino acids mentionedabove in relation to -A¹-. These functionalities may be protected withhydroxyl or amino protecting groups, as described herein.

An amino acid reside, such as amino acid residue -A¹-, where present,may be an amino acid residue where the side chain includes a nitrogenaromatic group, for example an imidazole group, as found in a histidineresidue. A nitrogen ring atom may be protected with an amino protectinggroup as described herein.

An amino acid reside, such as amino acid residue -A¹-, where present,may be an amino acid residue where the side chain includes carboxylfunctionality. This functionality may be protected with a carboxylprotecting group as described herein.

In certain embodiments of the invention, —R¹⁰ together with the carbonylgroup and nitrogen alpha to the carbon to which it is attached is anamino acid residue where the side chain includes hydroxyl functionality.An example of an amino acid residue including —R¹⁰ is threonine. Thehydroxyl functionality of this residue may be protected with a hydroxylprotecting group, as described herein.

In certain embodiments the —R^(T) or —R^(N) contains functionality suchas amino, hydroxyl carboxyl or thiol functionality. The amino, hydroxylcarboxyl or thiol functionality may be protected with amino, hydroxylcarboxyl or thiol protecting groups, as described herein.

Protecting groups, such as those for amino acid residues, are well knownand well described in the art.

Amino acids having side group protection, optionally together with aminoand carboxy protection, are commercially available. Thus, a protectedpolymyxin compound may be prepared from appropriately protected aminoacid starting materials.

Velkov et al. describe the step-wise preparation of polymyxin compoundson the solid-phase using suitably protected amino acid. The use ofprotected-forms of threonine and Dab is disclosed (see SupplementaryInformation).

As noted above, however, Velkov et al. do not describe the compounds offormula (II), for at least the reason that the amino acid residues atposition 6 are not exemplified in Velkov et al.

Where a protecting group is used is it is removable under conditionsthat do not substantially disrupt the structure of the polymyxin core,for example conditions that do not alter the stereochemistry of theamino acid residues.

In one embodiment, the protecting groups are acid-labile, base labile,or are removable under reducing conditions.

Example protecting groups for amino functionality include Boc(tert-butoxycabonyl), Bn (benzyl, Bzl), CbZ (Z), 2—CL-Z (2-chloro), Dde(1-[4,4-dimethyl-2,6-dioxocylcohex-1-ylidene]-3-methylbutyl), Fmoc(fluorenylmethyloxycarbonyl), HSO₃-Fmoc (sulfonylated Fmoc, such as2-sulfo-Fmoc, as described in e.g. Schechter et al, J. Med Chem 2002,45(19) 4264), ivDde (1-[4,4-dimethyl-2,6-dioxocylcohex-1-ylidene]ethyl),Mmt (4-methoxytrityl), Mtt (4-methyltrityl), Nvoc(6-nitroveratroyloxycarbonyl), and Tfa (trifluroacetyl).

Example protecting groups for aromatic nitrogen functionality includesBoc, Mtt, Trt and Dnp (dinitrophenyl).

In one embodiment, the protecting group for amino functionality isselected from Boc, CbZ, Bn and Fmoc and HSO₃-Fmoc.

In one embodiment, the protecting group for amino functionality is Boc,Fmoc or CbZ.

Example protecting groups for hydroxyl functionality include Trt(trityl), Bn (benzyl), tBu (tert-butyl), and2-acetamido-2-deoxy-3,4,6-tri-Oacetyl-α-galactopyranosyl.

In one embodiment, the protecting group for amino functionality is Trt.

Further example protecting groups include silyl ether protecting groups,such as TMS, TES, TBS, TIPS, TBDMS, and TBDPS. Such protecting groupsare removable with TBAF, for example.

Example protecting groups for carboxyl functionality include Bn (benzyl,Bz), tBu (tert-butyl), TMSET (trimethylsilylethyl) and Dmab({[4,4-dimethyl-2,6-dioxocylcohex-1-ylidene]-3-methylbutyl}aminobenzyl).

Example protecting groups for aromatic nitrogen functionality includesBoc, Mtt, Trt and Dnp (dinitrophenyl).

In some embodiments, only some types of functionality are protected. Forexample, only amino groups may be protected, such as amino groups in theside chain of an amino acid residue.

In one embodiment, amino groups and hydroxyl groups are protected.

Log P

A compound of the invention, such as a compound of formula (I) or (II),may have a partition-coefficient, such as expressed as a Log P value,within certain limits. The partition-coefficient may provide anindication of the lipophilicity of the compound.

A Log P value for a compound may be determined experimentally (forexample by partition of the compound between octanol and water), or itmay be predicted using standard computational methods. For example, areference to Log P may be a reference to ALog P, which may be determinedusing the methods described by Ghose et al. J. Phys. Chem. A, 1998, 102,3762-3772, the contents of which are hereby incorporated by reference intheir entirety. Thus, A Log P is the Ghose/Crippen group-contributionestimate for Log P.

In one embodiment, a compound has a Log P value, such as an A Log Pvalue, of at least−3.0, at least−3.5, at least−4.0, at least−6.0, atleast−6.3, at least−6.5, at least−6.7, or at least−7.0. In oneembodiment, a compound has a Log P value, such as an ALog P, value, ofat most−2.0, at most−3.0, at most−3.5, at most−4.0, at most−4.5, atmost−5.0, at most−5.2, at most−5.5, or at most−5.7.

In one embodiment, a compound has a Log P value within a range havingupper and lower limits appropriately selected from the limits givenabove, for example within the range−5.0 to −6.3, such as−5.5 to −6.3.

Compounds having Log P values, such as A Log P values, within the limitsdiscussed above are found to have excellent activity against bothpolymyxin-susceptible and polymyxin-resistant bacterial strains. Suchcompounds may also have reduced cytotoxicity compared with polymyxin B.

In another embodiment, a compound has a Log P value within a rangehaving upper and lower limits selected from the limits given above, forexample within the range−2.0 to −4.0, such as −2.0 to −3.5, such as−2.0to −3.0.

Compounds having Log P values, such as A Log P values, within the limitsdiscussed above are found to have optimum activity againstpolymyxin-resistant strains.

The present inventors have found that a compound having suitable Log Pvalues may be obtained by appropriate choice of N terminal group (suchas the choice of groups —R^(T) or —R^(N)) and amino acid residues atposition 6 and/or 7 (such as with appropriate selection of —R⁶ and/or—R⁷).

Polymyxin B

The deacylated from of the Polymyxin B decapeptide has the structureshown below:

where positions 1, 2, 4, 6, 7 and 10 are indicated (with reference tothe standard numbering system used for the Polymyxin B decapeptide), andthe amino acid residues are in the L-configuration, unless indicated.

Polymyxin B nonapeptide, octapeptides and heptapeptide forms are alsoknow in the art, and these compounds are truncated versions of thedecapeptide shown above

The compounds of the invention are variants of the polymyxin Bdecapeptide, nonapeptide, octapeptides and heptapeptide, where the aminoacid at positions 6 and/or positions 7 is substituted with another aminoacid, as described herein, and optionally the amino acid residues atpositions 2, 3 and 10 are substituted with another amino acid residue.

The compounds of formula (I) are compounds where the N terminal group ofthe polypeptide (which may be a decapeptide, a nonapeptide or other) ismodified.

The compounds of formula (II) are compounds where the N terminal aminogroup is optionally modified.

For convenience, the compounds of the invention are represented by theformula (I) where the amino acids at positions 1, 2, 3, 6, 7 or 10 aredetermined by the nature of the groups -A¹-, -A²- and -A³-, —R⁶, —R⁷ and—R¹⁰ respectively. Compounds of the invention, which include thevariants described above, are biologically active.

A variant of the compound is a compound in which one or more, forexample, from 1 to 5, such as 1, 2, 3 or 4 amino acids are substitutedby another amino acid. The amino acid may be at a position selected fromposition 6 and/or 7 and optionally positions 1, 2, 3, and 10 (referringto the numbering of residues used in polymyxin B). The substitution maybe for another amino acid or for a stereoisomer.

Methods of Preparation

Compounds of formula (I) and (II) be prepared by conventional peptidesynthesis, using methods known to those skilled in the art. Suitablemethods include solution-phase synthesis such as described by Yamada etal, J. Peptide Res. 64, 2004, 43-50, or by solid-phase synthesis such asdescribed by Velkov et al., ACS Chemical Biology, 9, 2014, 1172(including Supplementary Information), de Visser et al., J. Peptide Res,61, 2003, 298-306, and Vaara et al., Antimicrob. Agents andChemotherapy, 52, 2008. 3229-3236. These methods include a suitableprotection strategy, and methods for the cyclisation step.

As shown herein, it is possible to derivatise the N terminal group of adeacylated polymyxin compound, such as deacylated nonapeptides, withoutderivatising the amino groups that are present in the side chains of thepolymyxin compound. As described herein, the side chains of thepolymyxin compound may be selectively protected without protecting the Nterminal group. The N terminal group may then be reacted to provide theappropriate N terminal substituent. The side chain protection maysubsequently be removed.

The present inventors have also found that an amino acid at position 6or position 7 of a polymyxin compound may be modified in a method ofsynthesis, thereby providing a product polymyxin having a product havinga modified amino acid.

The inventors have identified halogenated phenylalanine amino acidresidues are useful intermediates for the preparation of modified aminoacids. The halogen group is a useful reactive functionality, and may besubstituted for other groups, for example in a cross-coupling reaction,such as a Suzuki-type cross-coupling reaction with a boronic acid orester, in the presence of a metal catalyst.

The present invention provides a compound of formula (II) where theamino acid residue at position 6 or position 7 contains a halogenatedphenyl group. However, the present invention is not limited to the useof such compounds, and variants of compound of formula (II) are alsoprovided, and are useful in synthesis. For example, the presentinvention also provides a compound of formula (III), which comprises ahalo aryl group.

In one embodiment, the method is the modification of phenylalanine.

In one embodiment of the invention there is provided a method ofpreparing a halogenated polymyxin compound, the method comprising thestep of treating a polymyxin compound with a halogenating agent, therebyto provide the halogenated polymyxin compound. Here, one the amino acidresidue at position 6 or position 7 contains an aryl group.

In one aspect there is provided a method of halogenating a polymyxincompound comprising an aryl group, such as an aryl group in an aminoacid residue, the method comprising treating the polymyxin compound witha halogenating agent. The product of the reaction is a polymyxincompound containing a haloaryl group, such as a haloaryl group in anamino acid residue. Such a compound may be referred to as a halogenatedpolymyxin compound.

In one embodiment, the polymyxin compound comprises a phenylalanine,tyrosine or histidine residue.

In one embodiment, the polymyxin compound comprises a phenylalanineresidue.

In one embodiment the method is the halogenation of a polymyxin compoundhaving a phenylalanine residue at position 6 or position 7.

The phenyl group of a phenylalanine residue may be halogenated at the4-position or the 2-position, or the reaction may produce a producthaving a mixture of the two. It is possible to separate 2- and4-halogenated products, for example by HPLC.

In one embodiment, the polymyxin compound comprises an α-amino acid,where the side chain of the amino acid comprises an aromatic group, suchas a carboaryl group. In one embodiment, the polymyxin compoundcomprises an α-amino acid, where the side chain of the amino acidcomprises a phenyl group, which is optionally substituted. In oneembodiment, the polymyxin compound comprises an α-amino acid, where theside chain of the amino acid comprises a benzyl group, which isoptionally substituted.

In one embodiment, there is provided a method for the preparation of apolymyxin compound of formula (IV), the method comprising the step oftreating an aryl-containing polymyxin compound of formula (III).

In one embodiment, the polymyxin compound of formula (III) and (IV) isrepresented thus:

wherein:

-T^(A) is hydrogen, C₁₋₄ alkyl or R^(N)—X—;

-A¹- is absent or is an amino acid residue;

-A²- is absent or is an amino acid residue;

-A³- is absent or is an amino acid residue;

—X— is —C(O)—, —NHC(O)—, —OC(O)—, —CH₂— or —SO₂—;

—R^(N) is a terminal group, such as a group —R^(T) as described herein;

—R⁶ together with the carbonyl group and nitrogen alpha to the carbon towhich it is attached is an amino acid residue;

—R⁷ together with the carbonyl group and nitrogen alpha to the carbon towhich it is attached is an amino acid residue;

and for the compounds of formula (IV) one of —R⁶ and —R⁷, comprises ahaloaryl group; and for the compounds of formula (III) one of —R⁶ and—R⁷, comprises an aryl group

R¹⁰ together with the carbonyl group and nitrogen alpha to the carbon towhich it is attached, is a threonine or leucine residue;

and salts, solvates, and/or protected forms thereof.

In one embodiment, —R⁶ comprises a haloaryl or an aryl group.

In one embodiment, —R⁷ comprises a haloaryl or an aryl group.

In one embodiment, -A¹-, -A²-, -A³- and R^(N)— do not contain anoptionally substituted aryl group.

In one embodiment, one of one of —R⁶ and —R⁷, comprises a benzyl group,where the phenyl is substituted with halo, such as monosubstituted.

In one embodiment, one of —R⁶ and —R⁷, comprises a haloaryl group.

In one embodiment, one of —R⁶ and —R⁷, comprises a bromoaryl group.

In one embodiment, the group —R^(N) is as defined for the compounds offormula (II).

In one embodiment, the polymyxin compound is Polymyxin B. Thus, —X— is—C(O)—, and —R^(N) is selected from 5-methylheptyl, 5-methylhexyl,heptyl, and hexyl.

In one embodiment, the group —R^(N) does not contain an aryl group, forexample does not contain a carboaryl or heteroaryl group.

In one embodiment, —R⁶ is benzyl for the compounds of formula (III), and—R⁶ is benzyl, where the phenyl group is substituted at the 2- or 4-position with halo, such as bromo (for the compounds of formula (IV)).

In one embodiment, the halogenation reaction is performed on a polymyxincompound where the side chain functionality of the amino acid residuesand optionally the functionality within —R^(N) is not protected. Theinventors have found that the halogenation reaction may beadvantageously performed directly on a polymyxin starting material,without the need to protect the amino acid functionality or protectfunctionality within —R^(N). Thus, a halogenated product may be producedfrom a polymyxin starting material in one step.

A halogenated polymyxin compound, such as compound (IV) may be preparedwithout the need for protecting groups. After such a compound isprepared ti may be necessary to protect the reactive functionality forfuture syntheses.

The compound of formula (III) may be reacted with a halogenating reagentto yield the compound of formula (IV).

In one embodiment, the halogenating reagent is a brominating reagent,and the product of the reaction is a brominated product.

In one embodiment, the halogenating reagent is N-halosuccinimide

In one embodiment, the halogenating reagent is selected from NBS(N-bromosuccinimide),

NCS (N-chlorosuccinimide), and NIS (N-iodosuccinimide).

In one embodiment, the halogenating reagent is NBS.

In one embodiment, the halogenating reagent is used in at least 1 moleequivalent with respect to the mole amount of aryl-containing compound.

In one embodiment, the halogenating reagent is used in at most 2 molesequivalent with respect to the mole amount of aryl-containing compound.

In one embodiment, the halogenating reagent is used at around 1.5 molesequivalent with respect to the mole amount of aryl-containing compound.

In one embodiment, the halogenating reagent is used together with aLewis acid.

In one embodiment, the Lewis acid is BF₃.

In one embodiment, the Lewis acid is selected from BF₃2H₂O and BF₃,2AcOH, such as

BF₃.2H₂O.

The Lewis acid may be a solvent for the reaction.

Additionally or attentively, H2O, CH3CN, AcOH may be present. Preferableno other solvent is present.

The halogenation reaction may be performed at ambient temperature, orbelow. Typically the halogenation reaction is performed at greater than5° C., as the preferred Lewis acids crystallise at temperatures below 5°C.

A halogenated polymyxin compound, such as compound (IV), is suitable foruse in methods of medical treatment as described herein. A halogenatedpolymyxin compound is also suitable for use as an intermediate in thepreparation of alternative polymyxin compounds, as described in furtherdetail below.

In one aspect of the invention, there is provided a method of synthesis,the method comprising the step of digesting a halogenated polymyxincompound selected from a halogenated decapeptide, a halogenatednonapeptide and a halogenated octapeptide, thereby to yield ahalogenated heptapeptide polymyxin compound. Digesting refers to step ofreducing the total number of amino acid residues within a polypeptide.

In one embodiment, a compound of formula (IVa) is digested to yield acompound of formula (IVb).

The compound of formula (IVa) is halogenated decapeptide, a halogenatednonapeptide or a halogenated octapeptide. The compound of formula (IVa)is a compound of formula (IV) where -A³- is an amino acid residue. Thecompound of formula (IVa) is a compound where —R⁶ or —R⁷ comprises ahaloaryl group. Following the cleavage reaction, the haloaryl group isretained in the cleaved product.

The compound of formula (IVb) is a halogenated heptapeptide polymyxincompound. The compound of formula (IVb) is a compound of formula (IV)where -A¹-, -A²-, and -A³- are absent and —T^(A) is hydrogen. Where thecompound of formula (IVa) is a compound where —R⁶ or —R⁷ comprises ahaloaryl group, it follows that the compound of formula (IVb) is acompound where —R⁶ or —R⁷ comprises a haloaryl group.

In one embodiment a protease is used in the digestion method, such as aserine protease, such as a subtilisin.

In one embodiment, Savinase is used to digest the halogenated polymyxincompound.

The compound of formula (IVb) is a useful intermediate for thepreparation of polymyxin compounds. The compound of formula (IVb) has anunmodified N terminal, and this terminal may be functionalised. Thecompound of formula (IVb) also has a haloaryl group, and the halogen maybe substituted with another group to give a substituted aryl group.

Accordingly, in one aspect there is provided a method of synthesis, themethod comprising the step of modifying the N terminal of a halogenatedheptapeptide polymyxin compound to yield a halogenated polymyxincompound having a halogenated decapeptide, a halogenated nonapeptide anda halogenated octapeptide, wherein the N terminal of the halogenateddecapeptide, a halogenated nonapeptide and a halogenated octapeptides isoptionally modified, and a halogenated heptapeptide having a modified Nterminal.

In one embodiment, the halogenated heptapeptide polymyxin compound is acompound of formula (IVb). The product of the reaction is a polymyxincompound of formula (V):

wherein:

-T^(A) is hydrogen, C₁₋₄ alkyl or R^(N)—X—;

-A¹- is absent or is an amino acid residue;

-A²- is absent or is an amino acid residue;

-A³- is absent or is an amino acid residue;

-   -   and where -A¹-, -A²-, and -A³- are absent, -T^(A) is C₁₋₄ alkyl        or R^(N)—X—;

—X— is —C(O)—, —NHC(O)—, —OC(O)—, —CH₂— or —SO₂—;

—R^(N) is a terminal group, such as a group —R^(T) as described herein;

—R⁶ together with the carbonyl group and nitrogen alpha to the carbon towhich it is attached is an amino acid residue;

—R⁷ together with the carbonyl group and nitrogen alpha to the carbon towhich it is attached is an amino acid residue;

and one of —R⁶ and —R⁷, together with the carbonyl group and nitrogenalpha to the carbon to which —R⁶ or —R⁷ is attached, is amino acidresidue having a haloaryl group;

R¹⁰ together with the carbonyl group and nitrogen alpha to the carbon towhich it is attached, is a threonine or leucine residue;

and salts, solvates, and/or protected forms thereof.

The compound (V) is typically formed from (IVb) by an amide couplingreaction. Thus, the terminal amino group in the compound of formula(IVb) is reacted with an appropriate carboxylic acid compound oractivated carboxylic compound to yield the amide product.

The carboxylic acid compound may be a compound of formula (IVc):

-   -   where -A¹-, -A²-, -A³- and —T^(A) have the same meanings as the        compounds of formula (V), and activated forms thereof.

In one embodiment, the reaction of a carboxylic acid with an amine maybe undertaken in the presence of one or more amide coupling reagents, asare well known in the art. A coupling reagent may optionally be usedtogether with a base, such as an organic base.

Amide coupling reagents suitable for use include carbodiimides (e.g. EDCand DCC), phosphonium salts (e.g. PyBOP), and uranium and guanidiniumsalts (e.g. HATU and HBTU), such as described in further detail below.

A carbodiimide may include dicyclohexylcarbodiimide (DCC),N-(3-dimethylaminopropyl)-N′-ethylcarbo-diimide (EDC),1-tert-butyl-3-ethylcarbodiimide,N-cyclohexyl-N′-2-morpholinoethyl)carbodiimide, anddiisopropylcarbodiimide.

A phosphonium salt may includebenzotriazol-1-yl-oxytripyrrolidinophosphonium hexafluorophosphate(PyBoP), (7-Azabenzotriazol-1-yloxy)tripyrrolidinophosphoniumhexafluorophosphate (PyAOP) and chlorotripyrrolidinophosphoniumhexafluorophosphate (PyBroP).

Uranium and guanidinium salts includeO-(Benzotriazol-1-yl)-N,N,N′,N′-tetramethyluronium hexafluorophosphate(HBTU), O-(Benzotriazol-1-yl)-N,N,N′,N′-tetramethyluroniumtetrafluoroborate (TBTU),O-(7-Azabenzotriazol-1-yl)-N,N,N′,N′-tetramethyluroniumhexafluorophosphate (HATU),N,N,N′,N′-tetramethyl-O-(N-succinimidyl)uronium tetrafluoroborate (TSTU)and O-[(ethoxycarbonyl)cyanomethylenamino]-N,N,N′,N′-tetramethyluroniumtetrafluoroborate (TNTU), amongst others.

Other agents may be used, including other benzotriazole-containingagents such as N-hydroxybenzotriazole (HOBt) and1-hydroxy-7-azabenzotriazole (HOAt), or reagents such as1-(mesitylene-2-sulfonyl)-3-nitro-1,2,4-triazole (MSNT) andpropylphosphonic anhydride (T3P).

Example coupling reagents are available from commercial sources, forexample as described in ChemFiles 2007, 4, No. 2, Sigma-Aldrich.

As noted above, the reaction of the acid and the carboxylic acid may beconducted in the presence of a base. Example bases include alkylaminebases such as N,N-diisopropylethylamine (DIPEA) and triethylamine (TEA),4-dimethylaminopyridine (DMAP), pyridine, and 4-methylmorpholine (NMM).

The amide-forming reaction may be performed in a solvent or solventmixture. A solvent for use may include dimethylformamide (DMF) anddichloromethane (DCM), toluene and acetonitrile. Other solvents, such asother alkyl formamides, halogenated hydrocarbons, aromatic hydrocarbonsand nitriles may be used as required.

The carboxylic acid compound used in the amide forming reaction may beinitially reacted with the amide coupling reagents to pre-form anactivated from of the carboxylic acid. The amine compound may then besubsequently added to the reaction mixture. This is not essential, andthe reaction components may be mixed in an alternative sequence, such asdescribed in the worked examples herein.

An activated form of the carboxylic acid includes an acyl halide, ahaloformate, an anhydride or a carboxylic ester. The carboxylic acid maybe reacted to form an acyl halide, haloformate, anhydride or carboxylicester by methods known in the art.

In one aspect of the invention, there is provided a method of synthesis,the method comprising the step of substituting a halogen within ahalogenated polymyxin compound to yield a polymyxin product having asubstituted aromatic group. The halogenated polymyxin compound is acompound having a haloaryl group.

In one embodiment, the halogenated heptapeptide polymyxin compound is acompound of formula (IV). The product of the reaction is a polymyxincompound of formula (VI):

wherein:

-T^(A) is hydrogen, C₁₋₄ alkyl or R^(N)—X—;

-A¹- is absent or is an amino acid residue;

-A²- is absent or is an amino acid residue;

-A³- is absent or is an amino acid residue; and where -A¹-, -A²-, and-A³- are absent, -T^(A) is C₁₋₄ alkyl or R^(N)—X—;

—X— is —C(O)—, —NHC(O)—, —OC(O)—, —CH₂— or —SO₂—; —R^(N) is a terminalgroup, such as a group —R^(T) as described herein;

—R⁶ together with the carbonyl group and nitrogen alpha to the carbon towhich it is attached is an amino acid residue;

—R⁷ together with the carbonyl group and nitrogen alpha to the carbon towhich it is attached is an amino acid residue;

and one of —R⁶ and —R⁷, comprises a substituted aryl group;

R¹⁰ together with the carbonyl group and nitrogen alpha to the carbon towhich it is attached, is a threonine or leucine residue;

and salts, solvates, and/or protected forms thereof.

In one embodiment, —R⁶ comprises a substituted aryl group, such as abenzyl group.

In one embodiment, —R⁷ comprises a substituted aryl group, such as abenzyl group.

The substitution reaction may be a cross-coupling reaction.

The substitution reaction may be a metal-catalysed substitutionreaction.

The substitution reaction may be a Pd-catalysed substitution reaction.

The substitution reaction may be a Suzuki-based coupling (substitution)reaction. Thus, the haloaryl-containing polymyxin compounds is reactedwith a boronic acid or ester in the presence of a metal catalyst toyield the substituted product.

In one embodiment, the substituted aryl group is aryl substituted with—R^(F), where —R^(F) is selected from optionally substituted C₁₋₁₂alkyl, optionally substituted C₂₋₁₂ alkenyl, optionally substitutedC₂₋₁₂ alkynyl, optionally substituted C₃₋₁₀ cycloalkyl, optionallysubstituted C₃₋₁₀ heterocyclyl, optionally substituted C₅₋₁₂ aryl, andan optionally subsitued group may have one or more substituent groupsselected from halo, haloalkyl, alkyl, alkenyl, alkynyl, and aryl, exceptthat alkyl alkenyl, and alkynyl groups are not substituents to the alkylalkenyl, and alkynyl groups. Suitable groups are described in relationto the definition of —R^(P) for —R⁶.

In one embodiment, the substituted aryl group is aryl substituted withoptionally substituted C₅₋₁₂ aryl.

Thus, the substitution reaction involves the reaction of a haloarylgroups with a reactive partner containing the group —R^(F). For example,the reactive partner is a boronic acid or ester comprising the group—R^(F).

A halogenated polymyxin compound having a modified N terminal may befurther reacted to yield a substituted polymyxin compounds having amodified N terminal.

In one aspect of the invention, there is provided a method of synthesis,the method comprising the step of substituting a halogen within ahalogenated polymyxin compound having a modified N terminal to yield apolymyxin product having a modified N terminal and a substitutedaromatic group. The halogenated polymyxin compound having a modified Nterminal is a compound having an amino acid residue with a haloarylgroup.

The term “substituted” as used herein with reference to a substitutionreaction refers to the formal replacement of the halogen group withanother group (which may be a different type of halogen group).

In one embodiment, the method is the replacement of the halogen groupwith a different halogen group.

The methods of the reaction allow a commercially available startingmaterial or a naturally-produced starting material to be converted to acompound of formula (I) or (II).

In a further aspect of the invention there is provided a method ofreducing an aryl-containing polymyxin compound, for example a method orreducing a compound of formula (III) or (VI), such as a protected formof (III) or (VI).

In one embodiment, the method comprises the step of contacting acompound of formula (III) or (VI), or protected forms thereof, with ametal catalyst in the present of hydrogen, thereby to reduce the arylgroup. The metal catalyst may be platinum oxide.

Such methods are particularly useful for the preparation ofcyclohexyl-containing compounds from phenyl-containing compounds, asexemplified herein.

Active Agent

The compounds of formula (I) or (II) may each be used together with asecond agent. The inventors have found that such combinations havegreater biological activity than would be expected from the individualactivity of both compounds. The compounds of formula (I) or (II) can beused to potentiate the activity of the second agent. In particular, thecompounds of formula (I) or (II) may be used together with a secondagent to enhance the antimicrobial activity of that agent, for exampleagainst Gram-negative bacteria.

Without wishing to be bound by theory it is believed that the compoundsof formula (I) or (II) act on the outer membrane of a cell e.g. aGram-negative bacterial cell, to facilitate the uptake of the secondagent into that cell. Thus, agents that are otherwise incapable or poorat crossing the outer membrane may be taken up into a target cell by theaction of the compounds of formula (I) or (II).

In one embodiment, the combination of a compound of formula (I) or (II)with the second agent is active against Gram-negative bacteria. Here, itis not essential that individually either of the compound of formula (I)or (II) or the second agent have activity against Gram-negativebacteria.

In one embodiment, the second agent is an agent having a measured MICvalue against a particular microorganism, such as a bacterium, that isless than 10, less than 5, or less than 1 micrograms/mL. Themicroorganism may be a Gram-negative bacteria, such as a Gram-negativebacteria selected from the group consisting of E. coli, S. enterica, K.pneumoniae, K. oxytoca; E. cloacae, E. aerogenes, E. agglomerans, A.calcoaceticus, A. baumannii; Pseudomonas aeruginosa, Stenotrophomonasmaltophila, Providencia stuartii, P. mirabilis, and P. vulgaris.

Examples of second agents that have activity against Gram-negativebacteria include beta-lactams, tetracyclines, aminoglycosides andquinolones.

In one embodiment, the second agent is an agent having a measured MICvalue against a particular microorganism, such as a Gram-negativebacterium, that is more than 4, more than 8, more than 16 or more than32 micrograms/mL. In this embodiment, the second agent may be activeagainst Gram-positive bacteria. For example, the second agent is anagent having a measured MIC value against a particular Gram-positivebacterium that is less than 10, less than 5, or less than 1micrograms/mL. Here, the compound of formula (I) or (II) acts tofacilitate the uptake of the second agent into the Gram-negativebacterial cell. The second agent is therefore able to act on a targetwithin the Gram-negative bacterial cell, which target may be the same asthe second agent's target in a Gram-positive bacterial cell.

The Gram-positive bacteria may be selected from the group consisting ofStaphylococcus and Streptococcus bacteria, such as S. aureus (includingMRSA), S. epidermis, E. faecalis, and E. faecium.

Examples of second agents that have activity against Gram-positivebacteria (at the MIC values given above, for example), and moderateactivity against Gram-negative bacteria, include rifampicin, novobiocin,macrolides, pleuromutilins. In one embodiment, a compound havingmoderate activity against Gram-negative bacteria may have a measured MICvalue against a Gram-negative bacterium that is less than 32, less than64, or less than 128 micrograms/mL.

Also suitable for use are agents having activity against Gram-positivebacteria and which are essentially inactive against Gram-negativebacteria. Examples include fusidic acid, oxazolidinines (e.g.linezolid), glycopeptides (e.g. vancomycin), daptomycin andIantibiotics. In one embodiment, a compound having essentially noactivity against Gram-negative bacteria may have a measured MIC valueagainst a Gram-negative bacterium that is more than 32, more then 64,more than 128, more than 256 micrograms/mL.

Under normal circumstances such agents are not necessarily suitable foruse against Gram-negative bacteria owing to their relatively poorability to cross the outer membrane of a Gram-negative bacterial cell.As explained above, when used together with a compound of formula (I) or(II), such agents are suitable for use.

In one embodiment, the active agent may be selected from the groupconsisting of rifampicin (rifampin), rifabutin, rifalazil, rifapentine,rifaximin, aztreonam, oxacillin, novobiocin, fusidic acid, azithromycin,ciprofloxacin, meropenem, tigecycline, erythromycin, clarithromycin andmupirocin, and pharmaceutically acceptable salts, solvates and prodrugforms thereof.

The present inventors have found that the polymyxin compounds of formula(I) or (II) may be used together with certain compounds in the rifamycinfamily to treat microbial infections. The rifamycin family includesisolates rifamycin A, B, C, D, E, S and SV, and syntheticallyderivatised versions of these compounds, such as rifampicin (rifampin),rifabutin, rifalazil, rifapentine, and rifaximin, and pharmaceuticallyacceptable salts and solvates thereof. In one embodiment, the activeagent is rifampicin (rifampin) and pharmaceutically acceptable salts,solvates and prodrug forms thereof.

Salts, Solvates and Other Forms

Examples of salts of compound of formula (I) and (II) include allpharmaceutically acceptable salts, such as, without limitation, acidaddition salts of strong mineral acids such as HCl and HBr salts andaddition salts of strong organic acids such as a methanesulfonic acidsalt. Further examples of salts include sulphates and acetates such astrifluoroacetate or trichloroacetate.

In one embodiment the compounds of the present disclosure are providedas a sulphate salt or a trifluoroacetic acid (TFA) salt. In oneembodiment the compounds of the present disclosure are provided asacetate salts.

A compound of formula (I) or (II) can also be formulated as prodrug.Prodrugs can include an antibacterial compound herein described in whichone or more amino groups are protected with a group which can be cleavedin vivo, to liberate the biologically active compound. In one embodimentthe prodrug is an “amine prodrug”. Examples of amine prodrugs includesulphomethyl, as described in e.g., Bergen et al, Antimicrob. Agents andChemotherapy, 2006, 50, 1953 or HSO3-FMOC, as described in e.g.Schechter et al, J. Med Chem 2002, 45(19) 4264, and salts thereof.Further examples of amine prodrugs are given by Krise and Oliyai inBiotechnology: Pharmaceutical Aspects, 2007, 5(2), 101-131.

In one embodiment a compound of formula (I) or (II) is provided as aprodrug.

A reference to a compound of formula (I) or (II), or any other compounddescribed herein, is also a reference to a solvate of that compound.Examples of solvates include hydrates.

A compound of formula (I) or (II), or any other compound describedherein, includes a compound where an atom is replaced by a naturallyoccurring or non-naturally occurring isotope. In one embodiment theisotope is a stable isotope. Thus a compound described here includes,for example deuterium containing compounds and the like. For example, Hmay be in any isotopic form, including ¹H, ²H (D), and ³H (T); C may bein any isotopic form, including ¹²C, ¹³C, and ¹⁴C; O may be in anyisotopic form, including ¹⁶O and ¹⁸O; and the like.

Certain compounds of formula (I) or (II), or any other compounddescribed herein, may exist in one or more particular geometric,optical, enantiomeric, diasteriomeric, epimeric, atropic,stereoisomeric, tautomeric, conformational, or anomeric forms, includingbut not limited to, cis- and trans-forms; E- and Z-forms; c-, t-, and r-forms; endo- and exo-forms; R—, S—, and meso-forms; D- and L-forms; d-and I-forms; (+) and (−) forms; keto-, enol-, and enolate-forms; syn-and anti-forms; synclinal- and anticlinal-forms; α- and β-forms; axialand equatorial forms; boat-, chair-, twist-, envelope-, andhalfchair-forms; and combinations thereof, hereinafter collectivelyreferred to as “isomers” (or “isomeric forms”).

Note that, except as discussed below for tautomeric forms, specificallyexcluded from the term “isomers,” as used herein, are structural (orconstitutional) isomers (i.e., isomers which differ in the connectionsbetween atoms rather than merely by the position of atoms in space). Forexample, a reference to a methoxy group, —OCH₃, is not to be construedas a reference to its structural isomer, a hydroxymethyl group, —CH₂OH.Similarly, a reference to ortho-chlorophenyl is not to be construed as areference to its structural isomer, meta-chlorophenyl. However, areference to a class of structures may well include structurallyisomeric forms falling within that class (e.g., C₁₋₆alkyl includesn-propyl and iso-propyl; butyl includes n-, iso-, sec-, and tert-butyl;methoxyphenyl includes ortho-, meta-, and para-methoxyphenyl).

Unless otherwise specified, a reference to a particular compoundincludes all such isomeric forms, including mixtures (e.g., racemicmixtures) thereof. Methods for the preparation (e.g., asymmetricsynthesis) and separation (e.g., fractional crystallisation andchromatographic means) of such isomeric forms are either known in theart or are readily obtained by adapting the methods taught herein, orknown methods, in a known manner.

One aspect of the present invention pertains to compounds insubstantially purified form and/or in a form substantially free fromcontaminants.

In one embodiment, the substantially purified form is at least 50% byweight, e.g., at least 60% by weight, e.g., at least 70% by weight,e.g., at least 80% by weight, e.g., at least 90% by weight, e.g., atleast 95% by weight, e.g., at least 97% by weight, e.g., at least 98% byweight, e.g., at least 99% by weight.

Unless specified, the substantially purified form refers to the compoundin any stereoisomeric or enantiomeric form. For example, in oneembodiment, the substantially purified form refers to a mixture ofstereoisomers, i.e., purified with respect to other compounds. In oneembodiment, the substantially purified form refers to one stereoisomer,e.g., optically pure stereoisomer. In one embodiment, the substantiallypurified form refers to a mixture of enantiomers. In one embodiment, thesubstantially purified form refers to an equimolar mixture ofenantiomers (i.e., a racemic mixture, a racemate). In one embodiment,the substantially purified form refers to one enantiomer, e.g.,optically pure enantiomer.

In one embodiment, the contaminants represent no more than 50% byweight, e.g., no more than 40% by weight, e.g., no more than 30% byweight, e.g., no more than 20% by weight, e.g., no more than 10% byweight, e.g., no more than 5% by weight, e.g., no more than 3% byweight, e.g., no more than 2% by weight, e.g., no more than 1% byweight.

Unless specified, the contaminants refer to other compounds, that is,other than stereoisomers or enantiomers. In one embodiment, thecontaminants refer to other compounds and other stereoisomers. In oneembodiment, the contaminants refer to other compounds and the otherenantiomer.

In one embodiment, the substantially purified form is at least 60%optically pure (i.e., 60% of the compound, on a molar basis, is thedesired stereoisomer or enantiomer, and 40% is the undesiredstereoisomer or enantiomer), e.g., at least 70% optically pure, e.g., atleast 80% optically pure, e.g., at least 90% optically pure, e.g., atleast 95% optically pure, e.g., at least 97% optically pure, e.g., atleast 98% optically pure, e.g., at least 99% optically pure.

Methods of Treatment

The compounds of formula (I) or (II), or pharmaceutical formulationscontaining these compounds, are suitable for use in methods of treatmentand prophylaxis. The compounds may be administered to a subject in needthereof. The compounds are suitable for use together with an activeagent (“a second active agent”), for example a second active agent thatis an antimicrobial agent.

The compounds of formula (I) or (II) are for use in a method oftreatment of the human or animal body by therapy. In some aspects of theinvention, a compound of formula (I) or (II) may be administered to amammalian subject, such as a human, in order to treat a microbialinfection.

Another aspect of the present invention pertains to use of a compound offormula (I) or (II) in the manufacture of a medicament for use intreatment. In one embodiment, the medicament comprises a compound offormula (I) or (II). In one embodiment, the medicament is for use in thetreatment of a microbial infection.

The term “microbial infection” refers to the invasion of the host animalby pathogenic microbes. This includes the excessive growth of microbesthat are normally present in or on the body of an animal. Moregenerally, a microbial infection can be any situation in which thepresence of a microbial population(s) is damaging to a host animal.Thus, an animal is “suffering” from a microbial infection when excessivenumbers of a microbial population are present in or on an animal's body,or when the presence of a microbial population(s) is damaging the cellsor other tissue of an animal.

The compounds may be used to treat a subject having a microbialinfection, or at risk of infection from a microorganism, such as abacterium.

The microbial infection may be a bacterial infection such as aGram-negative bacterial infection.

Examples of Gram-negative bacteria include, but are not limited to,Escherichia spp., Klebsiella spp., Enterobacter spp., Salmonella spp.,Shigella spp., Citrobacter spp., Morganella morganii, Yersiniapseudotuberculosis and other Enterobacteriaceae, Pseudomonas spp.,Acinetobacter spp., Moraxella, Helicobacter, Stenotrophomonas,Bdellovibrio, acetic acid bacteria, Legionella and alpha-proteobacteriasuch as Wolbachia and numerous others.

Medically relevant Gram-negative cocci include three organisms, whichcause a sexually transmitted disease (Neisseria gonorrhoeae), ameningitis (Neisseria meningitidis), and respiratory symptoms (Moraxellacatarrhalis).

Medically relevant Gram-negative bacilli include a multitude of species.Some of them primarily cause respiratory problems (Hemophilusinfluenzae, Klebsiella pneumoniae, Legionella pneumophila, Pseudomonasaeruginosa), primarily urinary problems (Escherichia coli, Enterobactercloacae), and primarily gastrointestinal problems (Helicobacter pylori,Salmonella enterica).

Gram-negative bacteria associated with nosocomial infections includeAcinetobacter baumannii, which causes bacteremia, secondary meningitis,and ventilator-associated pneumonia in intensive-care units of hospitalestablishments.

In one embodiment the Gram-negative bacterial species is selected fromthe group consisting of E. coli, S. enterica, K. pneumoniae, K. oxytoca;E. cloacae, E. aerogenes, E. agglomerans, A. calcoaceticus, A.baumannii; Pseudomonas aeruginosa, Stenotrophomonas maltophila,Providencia stuartii, P. mirabilis, and P. vulgaris.

In one embodiment the Gram-negative bacterial species is selected fromthe group consisting of E. colt, K. pneumoniae, Pseudomonas aeruginosa,and A. baumannii.

The compounds of formula (I) or (II) or compositions comprising the sameare useful for the treatment of skin and soft tissue infections,gastrointestinal infection, urinary tract infection, pneumonia, sepsis,intra-abdominal infection and obstetrical/gynaecological infections. Theinfections may be Gram-positive or Gram-negative bacterial infections.

The compounds of formula (I) or (II) or compositions comprising the sameare useful for the treatment of Pseudomonas infections including P.aeruginosa infection, for example skin and soft tissue infections,gastrointestinal infection, urinary tract infection, pneumonia andsepsis.

The compounds of formula (I) or (II) or compositions comprising the sameare useful for the treatment of Acinetobacter infections including A.baumanii infection, for pneumonia, urinary tract infection and sepsis.

The compounds of formula (I) or (II) or compositions comprising the sameare useful for the treatment of Klebsiella infections including K.pneumoniae infection, for pneumonia, urinary tract infection, meningitisand sepsis.

The compounds of formula (I) or (II) or compositions comprising the sameare useful for the treatment of E. coli infection including E. coliinfections, for bacteremia, cholecystitis, cholangitis, urinary tractinfection, neonatal meningitis and pneumonia.

The active agent may be an agent that has activity against themicroorganism. The active agent may be active against Gram-negativebacteria. The active agent may be active against a microorganismselected from the list given above.

In one embodiment, the second active agent has an MIC value of 10micrograms/mL or less against a microorganism such as E. coli, in theabsence of the compound of formula (I) or (II). The microorganism may bea microorganism selected from the group above.

Specific compounds for use as second active agents are described hereinand include:

-   -   rifampicin, rifabutin, rifalazil, rifapentine, and rifaximin;    -   oxacillin, methicillin, ampicillin, cloxacillin, carbenicillin,        piperacillin, tricarcillin, flucloxacillin, and nafcillin;    -   azithromycin, clarithromycin, erythromycin, telithromycin,        cethromycin, and solithromycin;    -   aztreonam and BAL30072;    -   meropenem, doripenem, imipenem, ertapenem, biapenem, tomopenem,        and panipenem;    -   tigecycline, omadacycline, eravacycline, doxycycline, and        minocycline;    -   ciprofloxacin, levofloxacin, moxifloxacin, and delafloxacin;    -   Fusidic acid;    -   Novobiocin;    -   teichoplanin, telavancin, dalbavancin, and oritavancin, and        pharmaceutically acceptable salts and solvates thereof;

In one embodiment, specific compounds for use as second active agentsare described herein and include rifampicin (rifampin), rifabutin,rifalazil, rifapentine, rifaximin, aztreonam, oxacillin, novobiocin,fusidic acid, azithromycin, ciprofloxacin, meropenem, tigecycline,erythromycin, clarithromycin and mupirocin, and pharmaceuticallyacceptable salts and solvates thereof.

In an alternative aspect, the compounds of formula (I) are suitable foruse in the treatment of fungal infections, for example in combinationtogether with an antifungal agent. The antifungal agent may be selectedfrom a polyene antifungal, for example amphotericin B, an imidazole,triazole, or thiazole antifungal, for example micaonazole, fluconazoleor abafungin, an allylamine, an echinocandin, or another agent, forexample ciclopirox.

Treatment

The term “treatment,” as used herein in the context of treating acondition, pertains generally to treatment and therapy, whether of ahuman or an animal (e.g., in veterinary applications), in which somedesired therapeutic effect is achieved, for example, the inhibition ofthe progress of the condition, and includes a reduction in the rate ofprogress, a halt in the rate of progress, alleviation of symptoms of thecondition, amelioration of the condition, and cure of the condition.Treatment as a prophylactic measure (i.e., prophylaxis) is alsoincluded. For example, use with patients who have not yet developed thecondition, but who are at risk of developing the condition, isencompassed by the term “treatment.”

The term “therapeutically-effective amount,” as used herein, pertains tothat amount of a compound, or a material, composition or dosage formcomprising a compound, which is effective for producing some desiredtherapeutic effect, commensurate with a reasonable benefit/risk ratio,when administered in accordance with a desired treatment regimen.

The term “treatment” includes combination treatments and therapies, asdescribed herein, in which two or more treatments or therapies arecombined, for example, sequentially or simultaneously.

Combination Therapy

A compound of formula (I) or (II) may be administered in conjunctionwith an active agent.

Administration may be simultaneous, separate or sequential.

The methods and manner of administration will depend on thepharmacokinetics of the compound of formula (I) or (II) and the secondagent.

By “simultaneous” administration, it is meant that a compound of formula(I) or (II) and a second agent are administered to a subject in a singledose by the same route of administration.

By “separate” administration, it is meant that a compound of formula (I)or (II) and a second agent are administered to a subject by twodifferent routes of administration which occur at the same time. Thismay occur for example where one agent is administered by infusion andthe other is given orally during the course of the infusion.

By “sequential” it is meant that the two agents are administered atdifferent points in time, provided that the activity of the firstadministered agent is present and ongoing in the subject at the time thesecond agent is administered.

Generally, a sequential dose will occur such that the second of the twoagents is administered within 48 hours, preferably within 24 hours, suchas within 12, 6, 4, 2 or 1 hour(s) of the first agent. Alternatively,the active agent may be administered first, followed by the compound offormula (I) or (II).

Ultimately, the order and timing of the administration of the compoundand second agent in the combination treatment will depend upon thepharmacokinetic properties of each.

The amount of the compound of formula (I) or (II) to be administered toa subject will ultimately depend upon the nature of the subject and thedisease to be treated. Likewise, the amount of the active agent to beadministered to a subject will ultimately depend upon the nature of thesubject and the disease to be treated.

Formulations

In one aspect, the present invention provides a pharmaceuticalcomposition comprising a compound of formula (I) or (II) together with apharmaceutically acceptable carrier. The pharmaceutical composition mayadditionally comprise a second active agent. In an alternativeembodiment, where a second agent is provided for use in therapy, thesecond agent may be separately formulated from the compound of formula(I) or (II). The comments below made in relation to the compound offormula (I) or (II) may therefore also apply to the second agent, asseparately formulated.

While it is possible for the compound of formula (I) or (II) to beadministered alone or together with the second agent, it is preferableto present it as a pharmaceutical formulation (e.g., composition,preparation, medicament) comprising at least one compound of formula (I)or (II), as described herein, together with one or more otherpharmaceutically acceptable ingredients well known to those skilled inthe art, including, but not limited to, pharmaceutically acceptablecarriers, diluents, excipients, adjuvants, fillers, buffers,preservatives, anti-oxidants, lubricants, stabilisers, solubilisers,surfactants (e.g., wetting agents), masking agents, colouring agents,flavouring agents, and sweetening agents. The formulation may furthercomprise other active agents, for example, other therapeutic orprophylactic agents.

Thus, the present invention further provides pharmaceuticalcompositions, as defined above, and methods of making a pharmaceuticalcomposition comprising admixing at least one compound of formula (I) or(II), as described herein, together with one or more otherpharmaceutically acceptable ingredients well known to those skilled inthe art, e.g., carriers, diluents, excipients, etc. If formulated asdiscrete units (e.g., tablets, etc.), each unit contains a predeterminedamount (dosage) of the compound. The composition optionally furthercomprises the second active agent in a predetermined amount.

The term “pharmaceutically acceptable,” as used herein, pertains tocompounds, ingredients, materials, compositions, dosage forms, etc.,which are, within the scope of sound medical judgment, suitable for usein contact with the tissues of the subject in question (e.g., human)without excessive toxicity, irritation, allergic response, or otherproblem or complication, commensurate with a reasonable benefit/riskratio. Each carrier, diluent, excipient, etc. must also be “acceptable”in the sense of being compatible with the other ingredients of theformulation.

Suitable carriers, diluents, excipients, etc. can be found in standardpharmaceutical texts, for example, Remington's Pharmaceutical Sciences,18th edition, Mack Publishing Company, Easton, Pa., 1990; and Handbookof Pharmaceutical Excipients, 5th edition, 2005.

The formulations may be prepared by any methods well known in the art ofpharmacy. Such methods include the step of bringing into association thecompound of formula (I) or (II) with a carrier which constitutes one ormore accessory ingredients. In general, the formulations are prepared byuniformly and intimately bringing into association the compound withcarriers (e.g., liquid carriers, finely divided solid carrier, etc.),and then shaping the product, if necessary.

The formulation may be prepared to provide for rapid or slow release;immediate, delayed, timed, or sustained release; or a combinationthereof.

Formulations may suitably be in the form of liquids, solutions (e.g.,aqueous, non-aqueous), suspensions (e.g., aqueous, non-aqueous),emulsions (e.g., oil-in-water, water-in-oil), elixirs, syrups,electuaries, mouthwashes, drops, tablets (including, e.g., coatedtablets), granules, powders, losenges, pastilles, capsules (including,e.g., hard and soft gelatin capsules), cachets, pills, ampoules,boluses, suppositories, pessaries, tinctures, gels, pastes, ointments,creams, lotions, oils, foams, sprays, mists, or aerosols.

Formulations may suitably be provided as a patch, adhesive plaster,bandage, dressing, or the like which is impregnated with one or morecompounds and optionally one or more other pharmaceutically acceptableingredients, including, for example, penetration, permeation, andabsorption enhancers. Formulations may also suitably be provided in theform of a depot or reservoir.

The compound may be dissolved in, suspended in, or admixed with one ormore other pharmaceutically acceptable ingredients. The compound may bepresented in a liposome or other microparticulate which is designed totarget the compound, for example, to blood components or one or moreorgans. Where a liposome is used, it is noted that the liposome maycontain both the compound of formula (I) or (II) and the second agent.

Formulations suitable for oral administration (e.g., by ingestion)include liquids, solutions (e.g., aqueous, non-aqueous), suspensions(e.g., aqueous, non-aqueous), emulsions (e.g., oil-in-water,water-in-oil), elixirs, syrups, electuaries, tablets, granules, powders,capsules, cachets, pills, ampoules, boluses.

Formulations suitable for buccal administration include mouthwashes,losenges, pastilles, as well as patches, adhesive plasters, depots, andreservoirs. Losenges typically comprise the compound in a flavouredbasis, usually sucrose and acacia or tragacanth. Pastilles typicallycomprise the compound in an inert matrix, such as gelatin and glycerin,or sucrose and acacia. Mouthwashes typically comprise the compound in asuitable liquid carrier.

Formulations suitable for sublingual administration include tablets,losenges, pastilles, capsules, and pills.

Formulations suitable for oral transmucosal administration includeliquids, solutions (e.g., aqueous, non-aqueous), suspensions (e.g.,aqueous, non-aqueous), emulsions (e.g., oil-in-water, water-in-oil),mouthwashes, losenges, pastilles, as well as patches, adhesive plasters,depots, and reservoirs.

Formulations suitable for non-oral transmucosal administration includeliquids, solutions (e.g., aqueous, non-aqueous), suspensions (e.g.,aqueous, non-aqueous), emulsions (e.g., oil-in-water, water-in-oil),suppositories, pessaries, gels, pastes, ointments, creams, lotions,oils, as well as patches, adhesive plasters, depots, and reservoirs.

Formulations suitable for transdermal administration include gels,pastes, ointments, creams, lotions, and oils, as well as patches,adhesive plasters, bandages, dressings, depots, and reservoirs.

Tablets may be made by conventional means, e.g., compression ormoulding, optionally with one or more accessory ingredients. Compressedtablets may be prepared by compressing in a suitable machine thecompound in a free-flowing form such as a powder or granules, optionallymixed with one or more binders (e.g., povidone, gelatin, acacia,sorbitol, tragacanth, hydroxypropylmethyl cellulose); fillers ordiluents (e.g., lactose, microcrystalline cellulose, calcium hydrogenphosphate); lubricants (e.g., magnesium stearate, talc, silica);disintegrants (e.g., sodium starch glycolate, cross-linked povidone,cross-linked sodium carboxymethyl cellulose); surface-active ordispersing or wetting agents (e.g., sodium lauryl sulfate);preservatives (e.g., methyl p-hydroxybenzoate, propyl p-hydroxybenzoate,sorbic acid); flavours, flavour enhancing agents, and sweeteners.Moulded tablets may be made by moulding in a suitable machine a mixtureof the powdered compound moistened with an inert liquid diluent. Thetablets may optionally be coated or scored and may be formulated so asto provide slow or controlled release of the compound therein using, forexample, hydroxypropylmethyl cellulose in varying proportions to providethe desired release profile. Tablets may optionally be provided with acoating, for example, to affect release, for example an enteric coating,to provide release in parts of the gut other than the stomach.

Ointments are typically prepared from the compound and a paraffinic or awater-miscible ointment base.

Creams are typically prepared from the compound and an oil-in-watercream base. If desired, the aqueous phase of the cream base may include,for example, at least about 30% w/w of a polyhydric alcohol, i.e., analcohol having two or more hydroxyl groups such as propylene glycol,butane-1,3-diol, mannitol, sorbitol, glycerol and polyethylene glycoland mixtures thereof. The topical formulations may desirably include acompound which enhances absorption or penetration of the compoundthrough the skin or other affected areas. Examples of such dermalpenetration enhancers include dimethylsulfoxide and related analogues.

Emulsions are typically prepared from the compound and an oily phase,which may optionally comprise merely an emulsifier (otherwise known asan emulgent), or it may comprises a mixture of at least one emulsifierwith a fat or an oil or with both a fat and an oil. Preferably, ahydrophilic emulsifier is included together with a lipophilic emulsifierwhich acts as a stabiliser. It is also preferred to include both an oiland a fat. Together, the emulsifier(s) with or without stabiliser(s)make up the so-called emulsifying wax, and the wax together with the oiland/or fat make up the so-called emulsifying ointment base which formsthe oily dispersed phase of the cream formulations.

Suitable emulgents and emulsion stabilisers include Tween 60, Span 80,cetostearyl alcohol, myristyl alcohol, glyceryl monostearate and sodiumlauryl sulfate. The choice of suitable oils or fats for the formulationis based on achieving the desired cosmetic properties, since thesolubility of the compound in most oils likely to be used inpharmaceutical emulsion formulations may be very low. Thus the creamshould preferably be a non-greasy, non-staining and washable productwith suitable consistency to avoid leakage from tubes or othercontainers. Straight or branched chain, mono- or dibasic alkyl esterssuch as di-isoadipate, isocetyl stearate, propylene glycol diester ofcoconut fatty acids, isopropyl myristate, decyl oleate, isopropylpalmitate, butyl stearate, 2-ethylhexyl palmitate or a blend of branchedchain esters known as Crodamol CAP may be used, the last three beingpreferred esters. These may be used alone or in combination depending onthe properties required. Alternatively, high melting point lipids suchas white soft paraffin and/or liquid paraffin or other mineral oils canbe used.

Formulations suitable for intranasal administration, where the carrieris a liquid, include, for example, nasal spray, nasal drops, or byaerosol administration by nebuliser, include aqueous or oily solutionsof the compound. As an alternative method of administration, a drypowder delivery may be used as an alternative to nebulised aerosols.

Formulations suitable for intranasal administration, where the carrieris a solid, include, for example, those presented as a coarse powderhaving a particle size, for example, in the range of about 20 to about500 microns which is administered in the manner in which snuff is taken,i.e., by rapid inhalation through the nasal passage from a container ofthe powder held close up to the nose.

Formulations suitable for pulmonary administration (e.g., by inhalationor insufflation therapy) include those presented as an aerosol sprayfrom a pressurised pack, with the use of a suitable propellant, such asdichlorodifluoromethane, trichlorofluoromethane,dichoro-tetrafluoroethane, carbon dioxide, or other suitable gases.Additionally or alternatively, a formulaton for pulmonary administrationmay be formulated for administration from a nebuliser or a dry powderinhaler. For example, the formulation may be provided with carriers orliposomes to provide a suitable particle size to reach the appropriateparts of the lung, to aid delivery of an appropriate does to enhanceretention in the lung tissue.

Formulations suitable for ocular administration include eye dropswherein the compound is dissolved or suspended in a suitable carrier,especially an aqueous solvent for the compound.

Formulations suitable for rectal administration may be presented as asuppository with a suitable base comprising, for example, natural orhardened oils, waxes, fats, semi-liquid or liquid polyols, for example,cocoa butter or a salicylate; or as a solution or suspension fortreatment by enema.

Formulations suitable for vaginal administration may be presented aspessaries, tampons, creams, gels, pastes, foams or spray formulationscontaining in addition to the compound, such carriers as are known inthe art to be appropriate.

Formulations suitable for parenteral administration (e.g., byinjection), include aqueous or non-aqueous, isotonic, pyrogen-free,sterile liquids (e.g., solutions, suspensions), in which the compound isdissolved, suspended, or otherwise provided (e.g., in a liposome orother microparticulate). Such liquids may additional contain otherpharmaceutically acceptable ingredients, such as anti-oxidants, buffers,preservatives, stabilisers, bacteriostats, suspending agents, thickeningagents, and solutes which render the formulation isotonic with the blood(or other relevant bodily fluid) of the intended recipient. Examples ofexcipients include, for example, water, alcohols, polyols, glycerol,vegetable oils, and the like. Examples of suitable isotonic carriers foruse in such formulations include Sodium Chloride Injection, Ringer'sSolution, or Lactated Ringer's Injection. Typically, the concentrationof the compound in the liquid is from about 1 ng/mL to about 100 μg/mL,for example from about 10 ng/mL to about 10 μg/mL, for example fromabout 10 ng/mL to about 1 μg/mL. The formulations may be presented inunit-dose or multi-dose sealed containers, for example, ampoules andvials, and may be stored in a freeze-dried (lyophilised) conditionrequiring only the addition of the sterile liquid carrier, for examplewater for injections, immediately prior to use. Extemporaneous injectionsolutions and suspensions may be prepared from sterile powders,granules, and tablets.

Dosage

Generally, the methods of the invention may comprise administering to asubject an effective amount of a compound of formula (I) or (II) so asto provide an antimicrobial effect. The compound of formula (I) or (II)may be administered at an amount sufficient to potentiate the activityof a second active agent. The second active agent is administered to asubject at an effective amount so as to provide an antimicrobial effect.

It will be appreciated by one of skill in the art that appropriatedosages of the compound of formula (I) or (II) or the active agent, andcompositions comprising the compound of formula (I) or (II) or theactive agent, can vary from patient to patient. Determining the optimaldosage will generally involve the balancing of the level of therapeuticbenefit against any risk or deleterious side effects. The selecteddosage level will depend on a variety of factors including, but notlimited to, the activity of the particular compound of formula (I) or(II) or the active agent, the route of administration, the time ofadministration, the rate of excretion of the compound, the duration ofthe treatment, other drugs, compounds, and/or materials used incombination, the severity of the condition, and the species, sex, age,weight, condition, general health, and prior medical history of thepatient. The amount of compound of formula (I) or (II) or the activeagent and route of administration will ultimately be at the discretionof the physician, veterinarian, or clinician, although generally thedosage will be selected to achieve local concentrations at the site ofaction which achieve the desired effect without causing substantialharmful or deleterious side-effects.

Administration can be effected in one dose, continuously orintermittently (e.g., in divided doses at appropriate intervals)throughout the course of treatment. Methods of determining the mosteffective means and dosage of administration are well known to those ofskill in the art and will vary with the formulation used for therapy,the purpose of the therapy, the target cell(s) being treated, and thesubject being treated. Single or multiple administrations can be carriedout with the dose level and pattern being selected by the treatingphysician, veterinarian, or clinician.

In general, a suitable dose of a compound of formula (I) or (II) or theactive agent is in the range of about 10 μg to about 250 mg (moretypically about 100 μg to about 25 mg) per kilogram body weight of thesubject per day. Where the compound of formula (I) or (II) or the activeagent is a salt, an ester, an amide, a prodrug, or the like, the amountadministered is calculated on the basis of the parent compound and sothe actual weight to be used is increased proportionately.

Kits

One aspect of the invention pertains to a kit comprising (a) a compoundof formula (I) or (II), or a composition comprising a compound asdefined in any one of formula (I) or (II), e.g., preferably provided ina suitable container and/or with suitable packaging; and (b)instructions for use, e.g., written instructions on how to administerthe compound or composition.

The written instructions may also include a list of indications forwhich the compound of formula (I) or (II) is a suitable treatment.

In one embodiment, the kit further comprises (c) a second active agent,or a composition comprising the second active agent. Here, the writteninstructions may also include a list of indications for which the secondactive agent, together with the compound of formula (I) or (II), issuitable for treatment.

Routes of Administration

A compound of formula (I) or (II), a second agent, or a pharmaceuticalcomposition comprising the compound of formula (I) or (II), or thesecond agent may be administered to a subject by any convenient route ofadministration, whether systemically/peripherally or topically (i.e., atthe site of desired action).

Routes of administration include, but are not limited to, oral (e.g., byingestion); buccal; sublingual; transdermal (including, e.g., by apatch, plaster, etc.); transmucosal (including, e.g., by a patch,plaster, etc.); intranasal (e.g., by nasal spray); ocular (e.g., byeyedrops); pulmonary (e.g., by inhalation or insufflation therapy using,e.g., via an aerosol, e.g., through the mouth or nose); rectal (e.g., bysuppository or enema); vaginal (e.g., by pessary); parenteral, forexample, by injection, including subcutaneous, intradermal,intramuscular, intravenous, intraarterial, intracardiac, intrathecal,intraspinal, intracapsular, subcapsular, intraorbital, intraperitoneal,intratracheal, subcuticular, intraarticular, subarachnoid, andintrasternal; by implant of a depot or reservoir, for example,subcutaneously or intramuscularly.

The Subject/Patient

The subject/patient may be a chordate, a vertebrate, a mammal, aplacental mammal, a marsupial (e.g., kangaroo, wombat), a rodent (e.g.,a guinea pig, a hamster, a rat, a mouse), murine (e.g., a mouse), alagomorph (e.g., a rabbit), avian (e.g., a bird), canine (e.g., a dog),feline (e.g., a cat), equine (e.g., a horse), porcine (e.g., a pig),ovine (e.g., a sheep), bovine (e.g., a cow), a primate, simian (e.g., amonkey or ape), a monkey (e.g., marmoset, baboon), an ape (e.g.,gorilla, chimpanzee, orang-utan, gibbon), or a human. Furthermore, thesubject/patient may be any of its forms of development, for example, afoetus.

In one preferred embodiment, the subject/patient is a human.

It is also envisaged that the invention may be practised on a non-humananimal having a microbial infection. A non-human mammal may be a rodent.Rodents include rats, mice, guinea pigs, chinchillas and othersimilarly-sized small rodents used in laboratory research.

Other Preferences

Each and every compatible combination of the embodiments described aboveis explicitly disclosed herein, as if each and every combination wasindividually and explicitly recited.

Various further aspects and embodiments of the present invention will beapparent to those skilled in the art in view of the present disclosure.

“and/or” where used herein is to be taken as specific disclosure of eachof the two specified features or components with or without the other.For example “A and/or B” is to be taken as specific disclosure of eachof (i) A, (ii) B and (iii) A and B, just as if each is set outindividually herein.

Unless context dictates otherwise, the descriptions and definitions ofthe features set out above are not limited to any particular aspect orembodiment of the invention and apply equally to all aspects andembodiments which are described. Where technically appropriateembodiments may be combined and thus the disclosure extends to allpermutations and combinations of the embodiments provided herein.

Certain aspects and embodiments of the invention will now be illustratedby way of example and with reference to the figures described above.

Examples

The following examples are provided solely to illustrate the presentinvention and are not intended to limit the scope of the invention, asdescribed herein.

Nomenclature—Compounds are named based on the natural polymyxin corefrom which they are synthetically derived.

Abbreviation Meaning PMBN Polymyxin B nonapeptide PMB Polymyxin B ThrThreonine Ser Serine DSer D-serine Leu Leucine Ile Isoleucine PhePhenylalanine Dphe D-phenylalanine Val Valine Dab α,γ-Diaminobutyricacid DIPEA N,N-diisopropylethylamine HATU2-(7-aza-1H-benzotriazol-1-yl)- 1,1-3,3-tetramethyluroniumhexafluorophosphate DCM Dichloromethane TFA Trifluoroacetic acid ND Notdetermined N/A Not applicable DMF N,N-Dimethylformamide PMBH Polymyxin Bheptapeptide (3-10) PMBD Polymyxin B decapepide Pro Proline Dapα,β-Diaminopropionic acid Gly Glycine His Histidine Phe PhenylalanineDCHA Dicyclohexylamine X phos 2-Dicyclohexylphosphino-2′,4′,6′-triisopropylbiphenyl NorLeu Norleucine NorVal Norvaline OctGly Octylglycine

Synthesis Examples

Comparator compounds C1 to C3 were prepared. Polymyxin B has aD-phenylalanine residue at position 6. The N terminal group is a6-methyloctanoyl group. Polymyxin B is readily available.

Compounds C1 and C2 have previously been prepared by the presentinventors. These compounds are polymyxin B nonapeptide derivatives. Thecompounds have a D-phenylalanine residue at position 6. The N terminalof the amino acid reside at position 2 is modified, as shown. Thepreparation of these compounds is described herein and is described inGB 1404301.2.

Compound C3 is a Polymyxin B variant differing from Polymyxin B in thesubstitution of the phenylalanine residue at position 6 with aD-(biphenyl)alanine residue (a D-(4-phenylphenyl)alanine residue).Compound C3 is structurally related close to the variants described byVelkov et al. C3 shares the same N terminal group as Polymyxin B(specifically Polymyxin B1), whilst Velkov et al. describes modified Nterminal group. Compound C₃ may be prepared by the methods described inVelkov et al. with appropriate replacement of the fatty acid in theterminal coupling step (see the Supporting Information for this paper).

In each of the worked examples 1-26, the amino acid at position 6 isreplaced with another amino acid. In some examples the amino acidresidue at position 1 is deleted, and the N terminal of the amino acidresidue at position 2 is modified, as shown.

Additional example compounds 27-79 are also provided, where the theamino acid at position 6 is replaced with another amino acid. In someexamples the amino acid residue at position 1 is deleted, and the Nterminal of the amino acid residue at position 2 is modified, as shown.

Additionally comparator compounds C4 to C7 were prepared.

The compounds for use in the present case are prepared as describedbelow. Each of the compounds has a polymyxin heptapeptide core (save forthe amino acid at position 6 or position 7). The compounds possess anL-Thr residue at the position corresponding to position 2 in polymyxinand an L-Dab or an L-Dap residue at the position corresponding toposition 3 in polymyxin (where L-Thr and L-Dab are the natural aminoacid residues present at these positions within Polymyxin B).

The compounds of the invention may be prepared by adaptation of thedetailed methods described below, and may also be prepared by adaptationof the methods described in WO 2015/135976, the contents of which arehereby incorporated by reference in their entirety. The methods used inthe present case also include those of WO 2013/072695 and WO2014/188178, the contents of which are hereby incorporated by referencein their entirety.

The compounds of the present invention differ from the compounds of WO2015/135976 in the nature of the amino acid residues at positions 6and/or 7 (i.e. in the nature of the groups —R⁶, —R^(6a), —R⁷, and—R^(7a)). However, the N terminal groups of the compounds of WO2015/135976 are suitable for use in the compounds of the invention. Thusa group —R^(T) or a group —R^(N) in the compounds of formula (I) or (II)of the present case may be a group —R¹⁵ as described in WO 2015/135976.

Therefore the description and exemplification of N terminalmodifications in WO 2015/135976 is relevant to the work in the presentcase. WO 2015/135976 shows that certain N terminal groups provideenhanced antibacterial activity and/or reduced cytotoxicity comparedwith wild type Polymyxin B (for example). Such N terminal groups may beused together with the amino acid substitutions at positions 6 and/or 7,as described by the inventors in the present case.

In particular, the present case incorporates by reference the detailedsynthesis examples of WO 2015/135976 from page 65 to page 90 (whichexamples are also present in GB 1421020.7 and GB 1516059.1, to which thepresent case claims priority).

Intermediate 5-Tri-(Boc) Polymyxin B heptapeptide

PMB sulphate (2 g) was dissolved in water (20 mL) followed by additionof 1,4-dioxane (40 mL) and left to stir for 10 minutes at roomtemperature. To the reaction mixture was added Boc anhydride (4.42 g)was added as solid and the reaction was stirred at room temperature andwas monitored by HPLC. The reaction mixture was then adjusted to pH 6using 1 M HCl , the precipitate which formed was filtered and washedwith water (50 mL) and heptane (50 mL), to leave Boc₅PMB as a whitesolid (2.4 g, 85%). This material (1 g) was dissolved in 1,4-butanediol(112.5 mL) and the mixture was stirred at 40° C. overnight. To thesolution potassium phosphate (75 mL, 0.12 5M pH 8.0) was added over oneminute, causing the formation of a white suspension. The reaction wasdiluted by adding 112.5 mL butanediol and 75 mL potassium phosphate(0.125 M pH 8.0), but the white emulsion persisted. The temperature ofthe reaction was reduced to 37° C. and then Savinase 16L (250 μL) wasadded and the reaction was stirred at room temperature overnight. As thereaction progressed the white emulsion cleared to form a transparentsolution due to the formation of the more soluble PMBH-Boc₃. Thereaction mixture was diluted with water (50 ml) and was then extractedwith DCM (100 mL) The DCM layer was collected and evaporated in vacuo toafford a colourless oil. The resulting oil was diluted in 50% methanol(aq.) and was loaded onto four preconditioned 10 g Varian Bond Elut SCXcartridges and the flow through was collected. The cartridges werewashed with two column volumes of 50% methanol (aq.) and then PMBH-Boc₃was eluted from the column using two column volumes of 20% ammonia inmethanol. The resulting eluent was evaporated to dryness in vacuo toafford purified PMBH-Boc₃ (610 mg). m/z 1062.6 [M+H]⁺.

Intermediate 7- Thr(O-^(t)Bu) Tetra-(N-Boc) Polymyxin B nonapeptide

Step 1-(S)-2-((S)-2-Benzyloxycarbonylamino-3-tert-butoxy-butyrylamino)-4-tert-butoxycarbonylamino-butyricacid methyl ester

To a stirred suspension of(S)-2-Benzyloxycarbonylamino-3-tert-butoxy-butyric acid DHCA salt (3.65g, 7.4 mmol) and (S)-2-Amino-4-tert-butoxycarbonylamino-butyric acidmethyl ester HCl salt (2.0 g, 7.4 mmol) in a mixture of DCM (60 mL) andDMF (120 mL) was added N,N-diisopropylethylamine (3.85 mL, 22.1 mmol).To this stirred mixture was added 1-hydroxy-7-azabenzotriazole (1.0 g,7.3 mmol) followed by N-(3-dimethylaminopropyl)-N′-ethylcarbodiimide HClsalt (1.42 g, 7.4 mmol). The mixture was stirred for 17 h at ambienttemperature then filtered under suction to remove the insolubleby-product, which was discarded. The filtrate was concentrated to ayellow oil which was partitioned between a solvent mixture of EtOAc/Et₂O(1:1) (250 mL) and 0.5 M hydrochloric acid (200 mL). The aqueous phasewas re-extracted with fresh solvent mixture (100 mL) and the combinedorganic extracts were successively washed with water (150 mL) and sat.NaHCO₃ solution (150 mL), dried (Na₂SO₄) and concentrated to acolourless oil (3.72g). This oil was purified by silica gelchromatography on a 100g SepPak cartridge, eluting with a solventgradient of EtOAc/i-hexane (0-70%). Fractions containing the product(R_(f) 0.26 in EtOAc/i-hexane 3:7, visualized with KMnO₄ spray) werepooled and concentrated to give the title compound as a colourless foam(3.58 g, 6.8 mmol, 92% yield). m/z 524 (MH⁺, 100%).

Step 2-(S)-2-((S)-2-Benzyloxycarbonylamino-3-tert-butoxy-butyrylamino)-4-tert-butoxycarbonylamino-butyricacid

A solution of lithium hydroxide monohydrate (0.861 g, 20.5 mmol) inwater (16 mL) was added to a stirred solution of(S)-2-((S)-2-Benzyloxycarbonylamino-3-tert-butoxy-butyrylamino)-4-tert-butoxycarbonylamino-butyricacid methyl ester (3.58 g, 6.8 mmol) in methanol (64 mL) at ambienttemperature and stirred for 19 h. To this solution was added 1M HCl (24mL) resulting in a milky mixture (pH 1) which was quickly extracted withDCM (3×135 mL). The combined organic extract was dried (Na₂SO₄) andconcentrated to give the title compound as a colourless foam (3.27 g,6.4 mmol, 94% yield).M/z 532[MNa]+, 1041 [2M+Na]+.

Step 3-CbzHNPMBN(OBu)(Boc)₄

(S)-2-((S)-2-Benzyloxycarbonylam ino-3-tert-butoxy-butyrylamino)-4-tert-butoxycarbonylam ino-butyric acid (1.73 g, 3.39 mmol) andTri-(N-Boc) Polymyxin B heptapeptide (prepared according to WO2012/168820, 3.0 g, 2.8 mmol) were charged to a flask to which dry DCM(85 ml) and dry DMF (17 mL) were added with stirring. To the stirredsolution was added N,N-diisopropylethylamine (1.46 ml, 8.4 mmol) andafter stirring for 5 min., O-(7-azabenzotriazol-1-yl)-N,N,N′N′-tetramethyluronium hexafluorophosphate (1.29 g, 3.39mmol) was added in a single portion. The mixture was sonicated for 2minutes then left to stir at ambient temperature for 18 h. The reactionmixture was then evaporated and the residue re-evaporated from toluene(3×100 mL). The residue was dried under vacuum for 3 h to ensure removalof toluene. Water (50 ml) was added to this material and the mixture wasrapidly stirred for 3 h with occasional sonication. The title compoundwas collected by suction filtration as a fine, white solid and washedwith water (2×25 mL) then dried under vacuum for 15h (4.6 g, 3.0 mmol,100% yield). m/z 1554[MH+].

Step 4-Title Compound

The product from step 3 (5.41 g, 3.48 mmol), ammonium formate (6.6 g,104.4 mmol) and 10% Pd—C (2.0 g) were charged to a flask under N2. MeOH(270 mL) was added and the mixture was stirred under N₂ for 4.5h. LCMSshowed MH⁺ for product and loss of starting material. The mixture wasfiltered under suction through a pad of celite and washed through withMeOH (50 mL). The filtrate and washings were evaporated to a colourlessoil which was partitioned between a solvent mixture of EtOAc/MeOH(4:1)(250 mL) and water (250 mL). The aqueous phase was furtherextracted with the same, fresh solvent mixture (2×100 mL). The combinedorganic extracts were dried (Na₂SO₄) and evaporated to a colourless oil(˜6 g). This material was purified by chromatography on silica gel (100g SepPak column) eluting with a gradient of MeOH/EtOAc (0-4%). Fractionscontaining the product (Rf 0.30 in EtOAc/MeOH/NH₄OH₈₈₀95:5:1, visualizedwith KMnO₄ spray) were pooled and evaporated to give the title compoundas a crispy foam (4.0 g, 2.8mmol, 81% yield). m/z 1420 [MH+].

Intermediate 11- Tetra- (N-Boc)-L-Thr(O-^(t)Bu)-L-Dap-Polymyxin Bheptapeptide

The title compound was prepared from(S)-2-((S)-2-Benzyloxycarbonylamino-3-tert-butoxy-butyrylamino)-3-tert-butoxycarbonylamino-propionicacid and Intermediate 5 according to the method for Intermediate 7 steps3 and 4. m/z 1405, [MH]⁺

Intermediate 16 (BOC)₃ D-[(4-Bromo)Phe]-6-Polymyxin heptapeptide and

Intermediate 17 (BOC)₃ D-[(2-Bromo)Phe]-6-Polymyxin heptapeptide

Step 1-D-[(4-Bromo)Phe]-6-Polymyxin and D-[(2-Bromo)Phe]-6-Polymyxin

Polymyxin B sulphate (source: Biotika) (20.0 g, 15.4 mmol) andN-bromosuccinimide (4.2 g, 23.6 mmol) were charged to a 1 L 3-neckround-bottomed flask, fitted with an efficient overhead paddle stirrerand a N₂ inlet. To the flask under N₂ was added boron trifluoridedihydrate (200 mL) and the mixture was vigorously stirred at ambienttemperature for 1 h during which time all solids dissolved to give afrothy, orange solution. The solution was then poured over 5 minutesinto a stirred mixture of ammonia 880 solution (400 mL) and ice (900 g)to give a white suspension. To the suspension (pH 9) was added water(300 mL) and the mixture was stirred at ambient temperature for 2h thenfiltered under suction through a large (20 cm diameter, porosity 2)glass sinter funnel. The solid was washed with water (200 mL) and suckedfree of excessive moisture. The material was then suspended in methanol(1.5 L) and re-evaporated to a residue. This was repeated with moremethanol (1.5 L) to afford a foam which was dried at ambient temperaturein vacuo for 3h (22.4 g) and identified as the title compound m/z=1282/4(MH⁺), 643 (M+2H)²⁺. The crude material was used without purification inthe next stage.

An aliquot was purified by preparative HPLC using the conditions ofGeneral method 1, to afford Example Compound 2 (data in Table)

Step 2-(Boc)₅ D-[(4-Bromo)Phe]-6-Polymyxin

Crude D-[(4-Bromo)Phe]-6-Polymyxin (15.4 mmol nominal amount, based onPolymyxin B sulphate used) was charged to a flask and acetonitrile (400mL) and water (200 mL) were added. To the stirred solution was addedtriethylamine (15 mL, 108 mmol), followed by a solution ofdi-tert-butyl-dicarbonate (23.5 g, 108 mmol) in acetonitrile (200 mL).The cloudy mixture was stirred at ambient temperature for 20 h. Thereaction mixture was then concentrated in vacuo and the residuere-evaporated from methanol (1 L) and dried. The dry residue was stirredwith a mixture of diethyl ether (75 mL) and iso-hexane (75 mL) for 0.5 hand the insoluble solid was filtered off under vacuum. The solid waspartitioned between dichloromethane/methanol (9:1) (400 mL) and 10%brine (300 mL). To the organic extract was added methanol (40 mL) andthe solution was washed with 10% brine (100 mL), dried (Na₂SO₄) andconcentrated in vacuo to a foam residue. This material was suspended indichloromethane/methanol (95:5) (140 mL) and left to stand for 0.5h. Themixture was filtered under suction to remove unwanted gelatinous solidand the filtrate was purified by column chromatography over silica gel,eluting with a gradient of dichloromethane/methanol to afford the titlecompound as a colourless foam (5.1 g) m/z 1782/4 (MH⁺). This partlypurified material was used directly in the next stage.

Step 3-(BOC)₃ D-[(4-Bromo)Phe]-6-Polymyxin heptapeptide and (BOC)₃D-[(2-Bromo)Phe]-6-Polymyxin heptapeptide

A suspension of crude (Boc)₅ D-[(4-Bromo)Phe]-6-Polymyxin (2.65 g, 1.49mmol) in 1,4-butanediol (76 mL) was stirred at 50° C. for 1h until athick solution was formed. Phosphate buffer solution (pH 8) (19 mL) wasadded and the stirred solution was cooled to 37° C. Savinase solution(Protease from Bacillus sp. Liquid>16 U/g, from Sigma Aldrich) (3 ml)was added and the viscous solution was stirred at 37° C. for 4 days. Thesolution was poured into a mixture of ethyl acetate (150 mL) and water(100 mL) and the whole was shaken vigorous. The aqueous layer wasre-extracted with ethyl acetate (50 mL) and the combined organicextracts were re-washed with water (2×75 mL), dried (Na₂SO₄) andevaporated in vacuo to afford an oil (1.94 g). This material wasdissolved in ethyl acetate/methanol (4:1) (10 mL) and the solutionpurified by column chromatography over silica gel eluting with agradient of Solvent A/ethyl acetate (0-60%) where SolventA=methanol/ammonia 880 solution (9:1). Relevant fractions were pooledand evaporated to a colourless foam (970 mg) identified as the titlecompound m/z 1140/2 (MH⁺).

Further purification by preparative HPLC (see Table A, General Method 1)afforded the pure title compound Intermediate 16, (BOC)3D-[(4-Bromo)Phe]-6-Polymyxin heptapeptide and Intermediate 17,D-[(2-Bromo)Phe]-6-Polymyxin heptapeptide. m/z 1140/2 (MH⁺).

Intermediate 18- (Cbz)(BOC)₄Thr(O¹Bu)-D-[(4-Bromo)Phe]-6-PMB nonapeptide

Prepared from Intermediate 16 and(S)-2-((S)-2-Benzyloxycarbonylamino-3-tert-butoxy-butyrylamino)-4-tert-butoxycarbonylamino-butyricacid using the method of Intermediate 7 step 3., to afford the titlecompound m/z 1633 (MH⁺).

Intermediate 19-(BOC)₄ Thr(OtBu)-L-Dap-(D—Cha-6)-PMB heptapeptide

Platinum oxide (200 mg) was added to a solution oftetra-(N-Boc)-L-Thr(O-^(t)Bu)-L-Dap-Polymyxin B heptapeptide(Intermediate 11) (1.8 g, 1.28 mmol) in acetic acid (80 mL). Hydrogengas was introduced and the reaction was stirred for 24 hours. Platinumoxide (400 mg) was added and the reaction stirred under hydrogen for afurther 48 hours. The solvent was evaporated and the crude material wasazeotroped with toluene (2×). The crude oil was dissolved in EtOAc andthen treated with Ambersep 900 (OH) resin. The resin was filtered off,washed with further EtOAc (2×) and the combined organics were evaporatedto afford the title compound as an off-white solid (1.76 g). MH⁺=1412.0,C₆₆H₁₁₈N₁₄O₁₉ requires 1411.7.

Intermediate 20-(BOC)₄ Thr(O¹Bu)-(D-Cha-6)-PMB nonapeptide

Prepared from Intermediate 7 (Thr(O-^(t)Bu) Tetra-(N-Boc) Polymyxin Bnonapeptide) using the conditions described above for the preparation ofIntermediate 19, to afford the title compound, MH⁺=1425.6, C₆₇H₁₂₀N₁₄O₁₉requires 1425.8.

General method 1: Preparation of nonapeptide amides

Step 1-The protected polymyxin nonapeptide (0.07 mmol) was dissolved indichloromethane (4 mL), and treated with the corresponding carboxylicacid (1.5 equiv. with respect to the polymyxin substrate),N,N-Diisopropylethylamine (3.0 equiv.), followed by HATU (2.0equivalent). After 16 h the completion of the reaction was confirmed byLC-MS and the reaction mixture was evaporated to dryness. Water (˜10 mL)was added and the mixture triturated then stirred vigorously for 1 h.The resultant precipitate was collected by filtration and dried in vacuoovernight.

Step 2 -The Boc-protected derivative from Step 1 was dissolved indichloromethane (3 mL) and treated with TFA (1 mL). The reaction mixturewas stirred at room temperature until LCMS confirmed completedeprotection. The solvent was evaporated and the residue chromatographedby preparative HPLC using the conditions in Table A:

TABLE A Prep HPLC conditions Column: Sunfire C18 OBD 5 μm × 30 mm × 150mm Mobile Phase A: Acetonitrile + 0.15% TFA Mobile Phase B: water +0.15% TFA Flow rate: 25 mL/min Gradient: Time 0 min  3% A 97% B Time 2min  3% A 97% B Time 25 min 40% A 60% B Time 30 min 97% A  3% B Time 32min 97% A  3% B Detection: 210 nm

Product-containing fractions were combined, evaporated to low volume,and lyophilised to afford the product as the TFA salt. Compound puritywas assessed by HPLC using the conditions outlined in Table B.

TABLE B Analytical HPLC conditions Column: Zorbax 5 μ C18 (2) 150 × 4.6mm Mobile Phase A: 10% Acetonitrile in 90% Water, 0.15% TFA Mobile PhaseB: 90% Acetonitrile in 10% Water, 0.15% TFA Flow rate: 1 mL/minGradient: Time 0 min 100% A  0% B Time 10 min  0% A 100% B Time 11 min 0% A 100% B Time 11.2 min 100% A  0% B Cycle time 15 min Injectionvolume: 20 μL Detection: 210 nmGeneral method 2: General method for the preparation of dipeptide amidederivatives of polymyxin B heptapeptide

In an alternative method, the carboxylic acid was coupled to a suitablyprotected amino acid methyl ester using HATU coupling conditions ofIntermediate 1 step 3. The methyl ester was hydrolysed as inIntermediate 1 step 2, then coupled to a suitably protected amino acidmethyl ester using HATU coupling conditions of Intermediate 7 step 1.After ester hydrolysis (Intermediate 7 step 2) , the acyl dipeptide wascoupled to the required polymyxin heptapeptide intermediate followed bydeprotection, as described in General Method 1, to afford the examplecompounds.

General method 3: Suzuki Coupling Method

Exemplified by the synthesis of (Cbz)(BOC)₄Thr(O^(t)Bu)-D-[(4-phenylphenyl)alanine]-6-PMB nonapeptide

To a solution of intermediate 18 (Cbz)(BOC)₄Thr(O^(t)Bu)-D-[(4-Bromo)Phe]-6-PMB nonapeptide, 605 mg, 0.371mmol) wasadded benzene boronic acid (68 mg, 0.556 mmol), palladium (II) acetate(8.3 mg, 0.0371 mmol), XPhos (35 mg, 0.0741 mmol) and potassiumphosphate tribasic (157 mg, 0.741 mmol) in toluene (10 mL) and thestirred mixture was degassed with nitrogen for 2 minutes. The reactionwas sealed and heated to 100° C. for 18 hours. After cooling the mixturewas diluted with EtOAc and water. The phases were separated and theaqueous layer was further extracted with 10% IPA in EtOAc. The combinedorganics were dried (MgSO₄) and the solvent evaporated to afford a crudeoil. This was purified by chromatography: 40 g column, using a gradientof 0 to 10% MeOH in EtOAc to afford the desired compound as a colourlessglass m/z 1630 (MH⁺).

General Method 4: Hydrogenation with Platinum Oxide

Exemplified by the synthesis of D-[Cyclohexyl]alanine-6-Polymyxin

A suspension of platinum oxide (20 mg, 0.088 mmol) in acetic acid (2 mL)was added to a stirred solution of polymyxin B (200 mg, 0.166 mmol) inacetic acid (20 mL). The reaction was hydrogenated for 24 h at ambienttemperature and atmospheric pressure. A further 200 mg Platinum oxidewas added portionwise during the course of the reaction. The reactionmixture was filtered through Celite and washed with water (100 mL). Thefiltrate was evaporated at reduced pressure to leave a beige solid. Thesolid was dissolved in water (2 mL) and purified by preparative HPLC asdescribed in the general method 1. Product containing fractions werecombined and lyophilised to afford the title compound as the TFA saltm/z 1209.8 (MH⁺), C₅₆H₁₀₄N₁₆O₁₃ exact mass 1208.80.

General Method 5: Catalytic Transfer Hydrogenation with Palladium onCarbon

Exemplified by the synthesis of(Trans-5-(isobutyl-piperidine)-3-carbonyl L-Thr-L-Dap-polymyxinD-[(4-octyl)Phe]-6-heptapeptide.

(Trans-5-(isobutyl -piperidine)-3-carbonyl L-Thr-L-Dap-polymyxinD-[(4-(E)-oct-1-enyl)Phe]-6-heptapeptide Isomer 1 was hydrogenated underthe conditions described for Intermediate 7 step 4 to afford the titlecompound. m/z 1228[MH⁺], 614[M+2H]²⁺. C₆₀H₁₀₅N₁₅O₁₂ requires 1227.81.

Example 24 Polymyxin B[D-(4-cyano)Phe]-6

A suspension of (Boc)₅ D-[(4-Bromo)Phe]-6-polymyxin (100 mg, 0.056mmol), Zinc cyanide (45 mg, 0.383 mmol, 6.8 mol equiv.) and1,1′-bis(diphenylphosphino)ferrocene (6 mg, 2 mol equiv.) in dry DMF (2ml) was degassed and then treated withtris(dibenzylideneacetone)dipalladium (0) (5 mg, 1 mol equiv). The tubewas sealed and heated to 100° C. for 3 days. The solvent was evaporatedand the residue partitioned between water and ethyl acetate. The organicphase was dried over anhydrous magnesium sulfate and evaporated. Theresidue was chromatographed on silica eluting with 0-10% (1% 0.880ammonia in methanol) in ethyl acetate, followed by further purificationby preparative HPLC eluting with 20-95% acetonitrile in water (plus 1%TFA). Product-containing fractions were combined and evaporated to anoil. This was dissolved in TFA (2 mL) and DCM (8 mL) and stirred at roomtemperature for 6 h. The solvent was evaporated and the residuelyophilized from water to afford the desired product as a white solid(2.8 mg) , m/z 614[M+2H]²⁺. C₅₇H₉₇N₁₇O₁₃ requires 1227.75.

Example 29 L-Dab-L-Thr-L-Dap-polymyxin [D-(4-octyl Phe)]-6 heptapeptide

Step 1. (BOC)₃ D-[(4-Bromo)Phe]-6-Polymyxin heptapeptide (Intermediate16) was coupled to(S)-2-((S)-2-Benzyloxycarbonylamino-3-tert-butoxy-butyrylamino)-3-tert-butoxycarbonylamino-propionicacid according to the method for Intermediate 7 step 3 to affordCBZ-Tetra-(N-Boc)-L-Thr(O-^(t)Bu)-L-Dap-Polymyxin B [D-(4-Bromo)Phe)]-6heptapeptide.

Step 2. CBZ-Tetra-(N-Boc)-L-Thr(O-^(t)Bu)-L-Dap-Polymyxin B[D-(4-Bromo)Phe)]-6 heptapeptide was treated with octenyl boronic acidunder the suzuki coupling conditions of General method 3, to afford CBZ-Tetra-(N-Boc)-L-Thr(O-^(t)Bu)-L-Dap-Polymyxin B [D-(4-oct-2-enyl)Phe)]-6heptapeptide.

Step 3. CBZ-Tetra-(N-Boc)-L-Thr(O-^(t)Bu)-L-Dap-Polymyxin B[D-(4-oct-2-enyl)Phe)]-6 heptapeptide was treated with ammonium formatein the presence of 10% Palladium on Carbon, as described forIntermediate 7, step 3 to affordTetra-(N-Boc)-L-Thr(O-^(t)Bu)-L-Dap-polymyxin B [D-(4-octyl)Phe)]-6heptapeptide.

Step 4 The product from Step 3 was coupled to(S)-2-((2-(benzyloxy)-2-oxoethyl)amino)-4-((tert-butoxycarbonyl)amino)butanoicacid DCHA salt under the standard coupling conditions of Intermediate 7step 3, to afford tetra-(N-BOC) L-Dab-L-Thr-L-Dap-polymyxin [D-(4-octylPhe)]-6 heptapeptide.

Step 5. The product from Step 4 was deprotected as described in theGeneral method 1 step 2 , followed by preparative HPLC to affords thetitle compound, L-Dab-L-Thr-L-Dap-polymyxin [D-(4-octyl Phe)]-6heptapeptide as a white solid m/z 1161[MH⁺], 581[M+2H]²⁺. C₅₄H₉₆N₁₆O₁₂requires 1160.74.

Synthesis of Carboxylic Acids

Carboxylic acids used for the assembly of polymyxin derivatives weresecured either via commercial sources, or prepared using methods knownto those skilled in the art. Experimental details of the followingcarboxylic acids serve as representative examples for the synthesis ofsimilar acid intermediates used in the synthesis of the compounds of thepresent invention.

4-(tert-Butoxycarbonylamino)-2-(4-chlorophenyl)butanoic acid

Step 1- Ethyl 2-(4-chlorophenyl)-2-oxo-acetate

To a solution of diethyl oxalate (1 mL, 7.36 mmol) in tetrahydofuran (10mL) at −50° C. was added 4-chlorophenylmagnesium bromide (1M solution indiethyl ether, 7.3 mL, 7.30 mmol). The reaction mixture was allowed towarm to −15° C. and stirred at that temperature for a further 1.5h. Thereaction was quenched by the addition of 1M hydrochloric acid (7 mL) andstirred at room temperature for 2 minutes. The layers were separated andthen the aqueous phase was further extracted with diethyl ether (×2).The combined organic phases were dried over magnesium sulphate, filteredand concentrated at reduced pressure to give the crude title compound asa yellow oil (1.63 g,>100%). m/z 235 (MNa⁺), C₁₀H₉ClO₃ exact mass212.02.

Step 2- Ethyl-2-(4-chlorophenyl)-3-cyano-prop-2-enoate

To a solution of crude ethyl 2-(4-chlorophenyl)-2-oxo-acetate (˜7.3mmol) in toluene (30 mL) was added(triphenylphosphoranylidene)acetonitrile (2.20 g, 7.30 mmol). Thereaction mixture was stirred at room temperature for 16 hours and thenconcentrated at reduced pressure. The product was purified by silica gelchromatography eluting with 0-40% ethyl acetate in iso-hexane to givethe title compound as a colourless oil (1.38 g, 81%). m/z 258 (MNa⁺),C₁₂H₁₀ClNO₂ exact mass 235.04.

Step 3- Ethyl 4-amino-2-(4-chlorophenyl)butanoate

To a solution of ethyl-2-(4-chlorophenyl)-3-cyano-prop-2-enoate (1.36 g,5.79 mmol) in methanol (60 mL) was added cobalt chloride (1.51 g, 11.6mmol). The reaction mixture was cooled to 0° C. and then treated withsodium borohydride (2.2 g, 57.8 mmol) portionwise. After the addition,the reaction was stirred at 0° C. for 1 hour. The mixture was quenchedby the addition of 1 M hydrochloric acid and stirred at room temperaturefor 20 minutes. The pH was adjusted to 11 by the addition of 880 ammoniaand then the mixture was filtered through a pad of celite which waswashed with dichloromethane. After separation of the layers, the aqueousphase was re-extracted with dichloromethane (×2). The combined organiclayers were dried over magnesium sulphate, filtered and concentrated togive the title compound as a pale brown oil (838 mg, 60%). m/z 242(MH⁺), C₁₂H₁₆ClNO₂ exact mass 241.09.

Step 4- Ethyl 4-(tert-butoxycarbonylamino)-2-(4-ch lorophenyl)butanoate

To a solution of ethyl 4-amino-2-(4-chlorophenyl)butanoate (836 mg, 3.47mmol) in dichloromethane (40 mL) was added di-tert-butyl dicarbonate(1.06 g, 4.86 mmol). The reaction mixture was stirred at roomtemperature for 16 hours and then concentrated at reduced pressure. Theproduct was purified by silica gel chromatography eluting with 0-40%ethyl acetate in iso-hexane to give the title compound as a colourlessoil (784 mg, 66%). m/z 364 (MNa⁺), C₁₇H₂₄CINO₄ exact mass 341.83.

Step 5-4-(tert-Butoxycarbonylamino)-2-(4-chlorophenyl)butanoic acid

To a solution of ethyl4-(tert-butoxycarbonylamino)-2-(4-chlorophenyl)butanoate (780 mg, 2.29mmol) in dioxane (10 mL) and water (10 mL) was added lithium hydroxidemonohydrate (300 mg, 7.14 mmol). The reaction mixture was stirred atroom temperature for 3 days and then concentrated at reduced pressure.The residue was partitioned between diethyl ether and water and the pHadjusted to 1 by the addition of 1 M hydrochloric acid. After separationof the layers, the aqueous phase was re-extracted with diethyl ether(×2). The combined organic phases were dried over magnesium sulphate,filtered and concentrated. The title compound was isolated as acolourless oil (663 mg, 93%). m/z 312 (M−H)⁻, C₁₅H₂₀ClNO₄ exact mass313.11.

(S)-2-(benzyloxy)-4-((tert-butoxycarbonyl)amino)butanoic acid

Step 1- Methyl (S)-2-(benzyloxy)-4-((tert-butoxycarbonyl)amino)butanoate

To a solution of methyl(S)-4-((tert-butoxycarbonyl)amino)-2-hydroxybutanoate (see Dewitt et al.Org. Biomol. Chem. 2011, 9, 1846) (233 mg, 1.0 mmol) in dry ethylacetate (10 mL) was added silver oxide (350 mg, 1.5 mmol) followed bybenzyl bromide (0.179 mL, 1.5 mmol). The mixture was stirred in the darkat room temperature overnight, then heated to 50° C. for 8 h. Themixture was cooled, filtered through Kieselguhr, and evaporated. Theresidue was chromatographed on silica eluting with 0-100% ethyl acetatein hexane to afford the desired product as a colourless oil (67 mg,20%). m/z 323.6. C17H25NO5 requires 323.17

Step 2- (S)-2-(benzyloxy)-4-((tert-butoxycarbonyl)amino)butanoic acid

Methyl (S)-2-(benzyloxy)-4-((tert-butoxycarbonyl)amino)butanoate (67 mg,0.2 mmol) was dissolved in water (1 mL) and dioxane (2 mL). Lithiumhydroxide (15 mg) was added and the mixture stirred at room temperatureovernight. The resultant mixture was concentrated under reducedpressure, diluted with water (4 mL) and washed with ethyl acetate. Theaqueous phase was adjusted to pH 2 with 1 M HCl and extracted withdichloromethane (3×4 mL). The dichloromethane extracts were combined andevaporated to give the title compounds as a white solid (40 mg, 64%).m/z 309.6 (MH+), 332 (MNa+). C16H23NO5 requires 309.16.

Additional Synthesis Examples

(S)-4-Amino-2-(cyclohexylmethoxy)butanoyl L-Thr-L-Dap-polymyxin[D-cyclohexylalanine-6]-heptapeptide (Compound 84)

(S)-4-Amino-2-(benzyloxy)butanoyl L-Thr-L-Dap-polymyxin[D-cyclohexylalanine-6]-heptapeptide trifluoroacetate salt (Example 42)(18 mg) was dissolved in isopropanol (5 mL) and water (1 mL), andtreated with 5% rhodium on alumina (10 mg). The mixture was stirredunder an atmosphere of hydrogen for 18 h. The catalyst was removed byfiltration and the filtrate purified by preparative HPLC using theconditions of General Method 3. Product-containing fractions werecombined, evaporated to low volume and lyophilized to a while solid (0.8mg). m/z 1153 [MH+], 1265 [M+TFA]+. C₅₃H₉₇N₁₅O₁₃ requires 1151.74.

Changes to Amino Acid Residues at Positions 6 and/or 7

Example compounds 94 to 99 (as shown in Table 1C below) were prepared bysolid phase peptide synthesis, with the cyclisation step carried outoff-resin. Suitable methodology is given in WO 2014/188178 (Example 50).An alternative method of solid phase synthesis is given in Velkov et aLand WO 2015/149131.

Structures depict the N-terminal group and side chain on the Polymyxinheptapeptide scaffold (PMBH, shown below). Relative stereochemistry isdepicted by heavy or dashed lines. Absolute stereochemistry is depictedby heavy or hashed wedged bonds.

The compounds described below have an L-Thr residue at the positioncorresponding to position 2 in polymyxin. The compounds have either anL-Dap or an L-Dab residue at the position corresponding to position 3 inpolymyxin.

The present case is based on GB 1421020.7, the contents of which arehereby incorporated by reference in their entirety. In that case thestereochemistry of the Thr residue at position 2 of some examplecompounds was incorrectly drawn. This is corrected in the examplecompounds presented in the present case. In context it is clear that theexample compounds, including the compounds of the invention, have anL-Thr residue at position 2 as the compounds are prepared indirectlyfrom polymyxin B, which retains L-Thr residue at position 2, or thecompounds are prepared from a polymyxin B heptapeptide which is coupledwith a L-Thr-containing group to ultimately yield the appropriateN-terminal-derivatised nonapeptide or decapeptide product.

It is noted also that the correct names for the example compounds wereused.

TABLE 1 R¹ HPLC (N-terminal and side-chain on Starting RT Exheptapeptide R² Formula Mass material Name (min) m/z PMB

C1

C52H89 N15O12 1115.7 Int 11 (trans-5-(isobutyl- piperidine)-3-carbonylL-Thr-L-Dap-polymyxin B heptapeptide 5.45 1117[MH+] 559[M + 2H]²⁺ C2

C51H88 N16O12 1116.7 Int 11 (S)-1-isobutyl piperazine-2-carbonyl-L-Thr-L-Dap-polymyxin B heptapeptide 5.12 1118[MH+] 559[M + 2H]²⁺ C3

C62H10 2N16O1 3 1278.7 (BOC)₅ polymyxin [D-(4- bromo Phe)]-6] PolymyxinB[D-(4- phenyl)Phe]-6] 6.67 1279.4[MH⁺] 640.3[M + 2H]²⁺ 1

C61H10 1N17O1 3 1279.77 6348 (BOC)₅ polymyxin [D-(4- bromo Phe)]-6Polymyxin B[D-(4-(4- pyridyl))Phe]-6] 5.64 1281[MH⁺] 641[M + 2H]²⁺ 2

C56H97 BrN16O 13 1280.66 0275 Polymyxin B Polymyxin B[D-(4-bromoPhe)]-6] 6.48 1282[MH⁺] 642[M + 2H]²⁺ 3

C58H93 N15O12 1191.71 2698 Int 16 (trans-5-(isobutyl-piperidine)-3-carbonyl L-Thr-L-Dap-polymyxin [D-(4-phenyl)Phe]-6]heptapeptide. Isomer 1 6.19 1193[MH⁺] 597[M + 2H]²⁺ 4

C58H93 N15O12 1191.71 2698 Int 16 (trans-5-(isobutyl-piperidine)-3-carbonyl L-Thr-L-Dap-polymyxin [D-(4-phenyl)Phe]-6]heptapeptide. Isomer 2 6.40 1193[MH⁺] 597[M + 2H]²⁺ 5

C57H92 N16O12 1192.71 Int 16 (S)-1-isobutyl piperazine-2-carbonyl-L-Thr-L-Dap-polymyxin [D-(4-phenyl)Phe]- 6]heptapeptide 6.14 1194[MH⁺]597[M + 2H]²⁺ 6

C62H10 2N16O1 2 1262.79 Int 16 (S)-1-octyl piperazine-2-carbonyl-L-Thr-L- Dap-polymyxin [D-(4- phenyl)Phe]- 6]heptapeptide6.75 1265[MH⁺] 632[M + 2H]²⁺ 7

C62H10 1N15O1 2 1247.78 Int 16 trans-4-octylpyrrolidine- 3-carbonylpolymyxin [D-(4-phenyl)Phe]-6] nonapeptide. Isomer 1 6.71 1248[MH⁺] 8

C62H10 1N15O1 2 1247.78 Int 16 trans-4-octylpyrrolidine- 3-carbonylpolymyxin [D-(4-phenyl)Phe]-6] nonapeptide. Isomer 2 7.04 1248[MH⁺]625[M + 2H]²⁺ 9

C62H10 1N15O1 2 1247.78 Int 17 trans-4-octylpyrrolidine- 3-carbonylpolymyxin [D-(2-phenyl)Phe]-6] nonapeptide. Isomer 1 6.70 1249[MH⁺]625[M + 2H]²⁺ 10

C62H10 1N15O1 2 1247.78 Int 17 trans-4-octylpyrrolidine- 3-carbonylpolymyxin [D-(2-phenyl)Phe]-6] nonapeptide. Isomer 2 7.08 1249[MH⁺]625[M + 2H]²⁺ 11

C52H88 BrN15O 12 1193.59 Int 16 (trans-5-(isobutyl-piperidine)-3-carbonyl L-Thr-L-Dap-polymyxin [D-(4-bromo Phe)]-6] heptapeptide Isomer 1 5.91 1195/1197 [MH⁺] 598[M + 2H]²⁺ 12

C52H88 BrN15O 12 1193.59 Int 16 (trans-5-(isobutyl-piperidine)-3-carbonyl L-Thr-L-Dap-polymyxin [D-(4-bromo Phe)]-6]heptapeptide Isomer 2 6.12 1195/1197 [MH⁺] 598[M + 2H]²⁺ 13

C49H84 BrN15O 12 1153.56 Int 16 2-aminomethyl-4- methyl pentanoylpolymyxin L-Thr-L-Dap- polymyxin [D-(4-bromo Phe)]-6]heptapeptide.Isomer 1 5.79 1155[MH⁺] 14

C49H84 BrN15O 12 1153.56 Int 16 2-aminomethyl-4- methyl pentanoylpolymyxin L-Thr-L-Dap- polymyxin [D-(4-bromo Phe)]-6]heptapeptide.Isomer 2 5.96 1155[MH⁺] 15

C55H89 N15O12 1151.68 Int 16 2-aminomethyl-4- mehtly pentanoyl polymyxinL-Thr-L-Dap- polymyxin [D-(4-phenyl Phe)]-6]heptapeptide. Isomer 1 6.211153[MH⁺] 16

C55H89 N15O12 1151.68 Int 16 2-aminomethyl-4- methyl pentanoyl polymyxinL-Thr-L-Dap- polymyxin [D-(4-phenyl Phe)]-6]heptapeptide. Isomer 2 6.361153[MH⁺] 17

C60H10 3N15O1 2 1225.79 Int 16 (trans-5-(isobutyl-piperidine)-3-carbonyl L-Thr-L-Dap-polymyxin [D-(4-(E)-oct-1-enyl)Phe]-6]heptapeptide Isomer 1 7.69 1226[MH⁺] 614[M + 2H]²⁺ 18

C60H10 3N15O1 2 1225.79 Int 16 (trans-5-(isobutyl-piperidine)-3-carbonyl L-Thr-L-Dap-polymyxin [D-(4-(E)-oct-1-enyl)-Phe]-6]heptapeptide Isomer 2 7.84 1226[MH⁺] 614[M + 2H]²⁺ 19

C56H88 F2N15O 12 1219.67 Int 16 2-Aminomethyl-4- methyl pentanoylpolymyxin L-Thr-L-Dap- polymyxin [D-{4-(4- trifluoromethyl) phenyl}Phe]-6]heptapeptide. Isomer 1 6.84 1221[MH⁺] 20

C56H88 F3N15O 12 1219.67 Int 16 2-Aminomethyl-4- methyl pentanoylpolymyxin L-Thr-L-Dap- polymyxin [D-{4-(4- trifluoromethyl) phenyl}Phe]-6]heptapeptide. Isomer 1 6.95 1221[MH⁺] 21

C50H93 N15O12 1095.71 2- amino- meth- yl pentanoyl polymyxin Bnonapeptide 2-Aminomethyl-4- methyl pentanoyl polymyxin D- [cyclohexylalanine]-6] nonapeptide. 5.84 1096.8[MH⁺] 22

C56H10 4N16O1 3 1208.80 Polymyxin B Polymyxin [D- cyclohexyl alanine]-6]6.54 1209.8[MH⁺] 23

C₆₀H₁₀₅ N₁₅O₁₂ 1227.81 Example 18 (Trans-5-(isobutyl-piperidine)-3-carbonyl L-Thr-L-Dap-polymyxin [D-(4-octyl Phe)]-6heptapeptide 7.99 1228[MH⁺] 614[M + 2H]²⁺ 24

C57H97 N17O13 1227.75 (Boc)₅ [D- (4- Bromo) Phe-6]- Polymyxin PolymyxinB[D-(4- cyano)Phe]-6 6.19 1229[MH⁺] 614[M + 2H]²⁺ 25

C56H97 N15O12 1171.74 Int 16 (Ttrans-5-(isobutyl- piperidine)-3-carbonylL-Thr-L-Dap-polymyxin [D-(4-isobutyl Phe)]- 6]heptapeptide isomer 2 6.761173[MH⁺] 587[M + 2H]²⁺ 26

C61H10 1N15O1 2C61H1 01N15O 12 1235.78 Int 16 2-(2-Aminoethyl)undecanoyl L-Thr-L-Dap-polymyxin [D-{4-(4-trifluoromethyl)phenyl}Phe]-6 heptapeptide. Isomer 2 7.38 1237[MH⁺] 619[M + 2H]²⁺

TABLE 1A Additional Synthesis Examples HPLC R¹ Starting RT Ex(N-terminal and side-chain on heptapeptide R² Formula Mass material Name(min) m/z C4

C51H89 N15O12 1103.68 Int 7 2-(2- Aminoethyl) hexanoyl polymyxin Bnonapeptide 5.31 1104.7 [MH⁺] C5

C53H93 N15O12 1131.71 Int 7 2-(2- Aminoethyl) octanoyl polymyxin Bnonapeptide 5.91 1132.7 [MH⁺] 567 [M + 2H]²⁺ C6

C52H91 N15O12 1117.70 Int 11 2-(2- Aminoethyl) octanoyl L- Thr-L-Dap-polymyxin heptapeptide 5.97 1161.2 [MH⁺] 27

C55H95 N15O12 1157.73 Int 16 2-(Aminomethyl)- 4- methylpentanoylL-Thr-L-Dap- polymyxin [D-(4- cyclohexyl Phe)]- 6 heptapeptide 6.85 1159[MH⁺] 580 [M + 2H]²⁺ 28

C51H93 N15O12 1107.71 Int 19 3-Amino-2- cyclohexylpropanoyl L-Thr-L-Dap-polymyxin [D- cyclohexylalanine]- 6 heptapeptide 6.05 1108.8 [MH⁺] 29

C54H96 N16O12 1160.74 Int 16 L-Dab-L-Thr-L- Dap-polymyxin [D-(4-octylPhe)]- 6 heptapeptide 7.50 1161 [MH⁺] 581 [M + 2H]²⁺ 30

C61H100 N16O12 1248.77 Int 16 (S)-1- Octylpiperazine- 2-carbonyl L-Thr-L-Dap-polymyxin [D-(4-phenyl Phe)]-6 heptapeptide. 6.73 1249.8 [MH⁺] 31

C52H95 N15O12 1121.73 Int 19 3-amino-2- (cyclohexylmethyl) propanoyl L-Thr-L-Dap- polymyxin [D- cyclohexylalanine]- 6 heptapeptide 6.08 1122.7[MH⁺] 32

C51H93 N15O12 1107.71 Int 19 3-amino-3- cyclohexylpropanoyl L-Thr-L-Dap-polymyxin [D- cyclohexylalanine]- 6 heptapeptide. Isomer 1 5.84 1108.8[MH⁺] 33

C51H93 N15O12 1107.71 Int 19 3-amino-3- cyclohexylpropanoyl L-Thr-L-Dap-polymyxin [D- cyclohexylalanine]- 6 heptapeptide. Isomer 2 5.93 1108.7[MH⁺] 34

C52H89 N15O12 1115.68 Int 19 3-amino-2- benzylpropanoyl L-Thr-L-Dap-polymyxin [D- cyclohexylalanine]- 6 heptapeptide. Isomer 2 5.95 1119[MH⁺] 559 [M + 2H]²⁺ 35

C53H91 N15O12 1129.70 Int 19 4-amino-2- benzylbutanoyl L-Thr-L-Dap-polymyxin [D- cyclohexylalanine]- 6 heptapeptide. Isomer 2 5.98 1131[MH⁺] 566 [M + 2H]²⁺ 36

C54H93 N15O12 1143.71 Int 20 4-amino-2- benzylbutanoyl- polymyxin [D-cyclohexylalanine]- 6 nonapeptide. isomer 2 5.97 1144 [MH⁺] 573 [M +2H]²⁺ 37

C55H100 N16O14 1208.76 Int 20 2-cyclohexyl-2- hydroxyacetyl polymyxin[D- cyclohexylalanine]- 6 nonapeptide 5.75 1209.6 [MH+] 606 [M + 2H]²⁺38

C52H89 N15O12 1115.68 Int 19 4-amino-2- phenylbutanoyl L-Thr-L-Dap-polymyxin [D- cyclohexylalanine]- 6 heptapeptide. isomer 2 5.72 1116.7[MH⁺] 39

C52H89 N15O12 1115.68 Int 19 4-amino-3- phenylbutanoyl L-Thr-L-Dap-polymyxin [D- cyclohexylalanine]- 6 heptapeptide. 5.70 1116.7 [MH⁺] 40

C51H95 N15O12 1109.73 Int 20 2-(2- aminoethyl) hexanoyl [D-cyclohexylalanine]- 6 nonapeptide. 5.76 1111 [MH⁺] 556 [M + 2H]²⁺ 41

C50H93 N15O12 1095.71 Int 19 2-(2- aminoethyl) hexanoyl L-Thr-L-Dap-polymyxin [D- cyclohexylalanine]- 6 heptapeptide. Isomer 2 5.84 1097[MH⁺] 549 [M + 2H]²⁺ 42

C52H95 N15O12 1121.73 Int 19 4-amino-3- cyclohexylbutanoyl L-Thr-L-Dap-polymyxin [D- cyclohexylalanine]- 6 heptapeptide. Isomer 1 5.88 1122.7[MH⁺] 43

C52H95 N15O12 1121.73 Int 19 4-amino-3- cyclohexylbutanoyl L-Thr-L-Dap-polymyxin [D- cyclohexylalanine]- 6 heptapeptide. isomer 2 5.95 1122.7[MH⁺] 44

C52H88 FN15O12 1133.67 Int 19 4-amino-2-(4- fluorophenyl) butanoylL-Thr-L- Dap-polymyxin [D- cyclohexylalanine]- 6 heptapeptide. Isomer 25.75 1135 [MH⁺] 568 [M + 2H]²⁺ 45

C53H90 FN15O12 1147.69 Int 19 4-amino-2-(3- fluorobenzyl) butanoylL-Thr-L- Dap-polymyxin [D- cyclohexylalanine]- 6 heptapeptide. isomer 25.90 1149 [MH⁺] 575 [M + 2H]²⁺ 46

C50H93 N15O13 1111.71 Int 19 (S)-4-amino-2- butoxybutanoyl L-Thr-L-Dap-polymyxin [D- cyclohexylalanine]- 6 heptapeptide. 5.64 1113 [MH⁺] 557[M + 2H]²⁺ 47

C51H95 N15O12 1109.73 Int 19 2-(2-aminoethyl)- 4-methylhexanoylL-Thr-L-Dap- polymyxin [D- cyclohexylalanine]- 6 heptapeptide. Isomer 25.91 1111 [MH⁺] 556 [M + 2H]²⁺ 48

C53H91 N15O13 1145.69 Int 19 (S)-4-amino-2- (benzyloxy) butanoylL-Thr-L-Dap- polymyxin [D- cyclohexylalanine]- 6 heptapeptide. 5.721146.7 [MH⁺] 1259 [M + TFA] 49

C52H98 N16O12 1138.76 Int 19 (S)-4-amino-2- (hexylamino) butanoylL-Thr-L- Dap-polymyxin [D- cyclohexylalanine]- 6 heptapeptide. 5.891139.6 [MH⁺] 50

C52H88 ClN15O12 1149.64 Int 19 4-amino-3-(4- chlorophenyl) butanoylL-Thr-L- Dap-polymyxin [D- cyclohexylalanine]- 6 heptapeptide. Isomer 15.61 1150.5 [MH⁺] 51

C52H88 ClN15O12 1149.64 Int 19 4-amino-3-(4- chlorophenyl) butanoylL-Thr-L- Dap-polymyxin [D- cyclohexylalanine]- 6 heptapeptide. Isomer 25.66 1150.4 [MH⁺] 52

C52H96 N16O12 1136.74 Int 20 (S)-1- isobutylpiperazine- 2-carbonylpolymyxin [D- cyclohexylalanine]- 6 nonapeptide 5.50 1137 [MH⁺] 570 [M +2H]²⁺ 53

C53H91 N15O12 1129.70 Int 20 3-amino-2- benzylpropanoyl polymyxin [D-cyclohexylalanine]- 6 nonapeptide. Isomer 2 5.87 1131 [MH⁺] 566 [M +2H]²⁺ 54

C53H90 FN15O12 1147.69 Int 20 4-amino-2-(4- fluorophenyl) butanoylpolymyxin [D- cyclohexylalanine]- 6 nonapeptide isomer 2 5.84 1149 [MH⁺]575 [M + 2H]²⁺ 55

C53H90 ClN15O12 1163.66 Int 20 4-amino-2-(3- chlorophenyl) butanoylpolymyxin [D- cyclohexylalanine]- 6 nonapeptide. isomer 2 5.95 1164[MH⁺] 56

C53H91 N15O12 1129.70 Int 20 4-amino-3- phenylbutanoyl polymyxin [D-cyclohexylalanine]- 6 nonapeptide isomer 1 5.57 1130.5 [MH⁺] 57

C53H91 N15O12 1129.70 Int 20 4-amino-3- phenylbutanoyl polymyxin [D-cyclohexylalanine]- 6 nonapeptide isomer 2 5.60 1130.5 [MH⁺] 58

C53H91 N15O12 1129.70 Int 19 4-amino-3- benzylbutanoyl L-Thr-L-Dap-polymyxin [D- cyclohexylalanine]- 6 heptapeptide. Isomer 1 5.83 1131[MH⁺] 566 [M + 2H]²⁺ 59

C53H91 N15O12 1129.70 Int 19 4-amino-3- benzylbutanoyl L-Thr-L-Dap-polymyxin [D- cyclohexylalanine]- 6 heptapeptide. Isomer 2 5.90 1131[MH⁺] 566 [M + 2H]²⁺ 60

C52H89 N15O12 1115.68 Int 19 4-amino-4- phenylbutanoyl L-Thr-L-Dap-polymyxin [D- cyclohexylalanine]- 6 heptapeptide. Isomer 1 5.67 1118[MH⁺] 559 [M + 2H]²⁺ 61

C52H89 N15O12 1115.68 Int 19 4-amino-4- phenylbutanoyl L-Thr-L-Dap-polymyxin [D- cyclohexylalanine]- 6 heptapeptide. Isomer 2 5.69 1117[MH⁺] 559 [M + 2H]²⁺ 62

C53H90 FN15O12 1147.69 Int 20 3-amino-2-(2- fluorobenzyl) propanoyl 5.851150 [MH⁺] 575 [M + 2H]²⁺ 63

C52H95 N15O12 1121.73 Int 19 4-amino-4- cyclohexylbutanoyl L-Thr-L-Dap-polymyxin [D- cyclohexylalanine]- 6 heptapeptide. 5.81 1123 [MH⁺] 562[M + 2H]²⁺ 64

C53H91 N15O12 1129.70 Int 20 4-amino-2- phenylbutanoyl polymyxin [D-cyclohexylalanine]- 6 nonapeptide isomer 2 5.72 1130.5 [MH⁺] 65

C53H90 FN15O12 1147.69 Int 19 4-amino-2-(2- fluorobenzyl) butanoylL-Thr-L- Dap-polymyxin [D- cyclohexylalanine]- 6 heptapeptide. Isomer 25.90 1149 [MH⁺] 66

C54H93 N15O12 1143.71 Int 20 4-amino-3- benzylbutanoyl polymyxin [D-cyclohexylalanine]- 6 nonapeptide isomer 1 5.71 1146 [MH⁺] 573 [M +2H]²⁺ 67

C54H93 N15O12 1143.71 Int 20 4-amino-3- benzylbutanoyl polymyxin [D-cyclohexylalanine]- 6 nonapeptide isomer 2 5.79 1145 [MH⁺] 573 [M +2H]²⁺ 68

C51H89 N15O12S 1135.65 Int 19 4-amino-2- (thiophen-3- ylmethyl)butanoylL-Thr-L-Dap- polymyxin [D- cyclohexylalanine]- 6 heptapeptide. 5.77 1138[MH⁺] 570 [M + 2H]²⁺ 69

C53H97 N15O12 1135.74 Int 20 4-amino-2- cyclohexylbutanoyl polymyxin [D-cyclohexylalanine]- 6 nonapeptide isomer 2 7.86 1136.6 [MH⁺] 70

C51H89 N15O12S 1135.65 Int 20 4-amino-2- (thiophen-2- yl)butanoylpolymyxin [D- cyclohexylalanine]- 6 nonapeptide isomer 2 5.71 1137 [MH⁺]569 [M + 2H]²⁺ 71

C54H93 N15O13 1159.71 Int 19 (S)-4-amino-2- ((4- methylbenzyl)oxy)butanoyl L-Thr- L-Dap-polymyxin [D- cyclohexylalanine]- 6 heptapeptide.5.95 1160.6 [MH⁺] 1273 [M + TFA]⁺ 72

C54H99 N15O12 1149.76 Int 20 4-amino-3- (cyclohexylmethyl) butanoylpolymyxin [D- cyclohexylalanine]- 6 nonapeptide 6.27 1150.5 [MH⁺] 73

C53H97 N15O12 1135.74 Int 20 (trans-5-(isobutyl- piperidine)-3- carbonylpolymyxin [D- cyclohexylalanine]- 6 nonapeptide 6.15 1136.6 [MH⁺] 74

C53H90 ClN15O13 1179.65 Int 19 (S)-4-amino-2-((4- chlorobenzyl)oxy)butanoyl L-Thr- L-Dap-polymyxin [D- cyclohexylalanine]-6 heptapeptide.6.16 1180.5 [MH⁺] 1293.5 [M + TFA]⁺ 75

C52H95 N15O12 1121.73 Int 19 4-amino-2- (cyclopentylmethyl) butanoyl L-Thr-L-Dap- polymyxin [D- cyclohexylalanine]- 6 heptapeptide. 6.15 1123[MH⁺] 562 [M + 2H]²⁺ 76

C52H88 ClN15O12 1149.64 Int 19 4-amino-2-(2- chlorophenyl) butanoylL-Thr-L- Dap-polymyxin [D- cyclohexylalanine]- 6 heptapeptide. 6.01 1151[MH⁺] 77

C53H90 ClN15O12 1163.66 Int 20 4-amino-2-(2- chlorophenyl) butanoylpolymyxin [D- cyclohexylalanine]- 6 nonapeptide 5.97 1166 [MH⁺] 583 [M +2H]²⁺ 78

C53H91 N15O13 1145.69 Int 19 (S)-3-amino-2-((4- methylbenzyl)oxy)propanoyl L-Thr- L-Dap-polymyxin [D- cyclohexylalanine]- 6 heptapeptide6.09 1146.7 [MH⁺] 79

C52H88 ClN15O12 1149.64 Int 19 4-Amino-2-(3- chlorophenyl) butanoylL-Thr-L- Dap-polymyxin [D- cyclohexylalanine]- 6 heptapeptide. 5.89 1151[MH⁺] 576 [M + 2H]²⁺

TABLE 1B Further Additional Synthesis Examples HPLC R¹ Starting RT Ex(N-terminal and side-chain on heptapeptide R² Formula Mass material Name(min) m/z 80

C51H95 N15O12 1109.73 Int 19 2-(2-aminoethyl)- 5- methylhexanoylL-Thr-L-Dap- polymyxin [D- cyclohexylalanine- 6]heptapeptide. isomer 25.93 1111 [MH⁺] 81

C52H88 ClN15O13 1165.64 Int 19 (S)-3-amino-2- ((4- chlorobenzyl)oxy)propanoyl L-Thr- L-Dap-polymyxin [D- cyclohexylalanine- 5.97 1167 [MH⁺]6]heptapeptide 82

C53H90 ClN15O13 1179.65 Int 19 4-amino-2-((3- chlorobenzyl)oxy) butanoylL-Thr- L-Dap-polymyxin [D- cyclohexylalanine- 6]heptapeptide. Isomer 15.93 1180 [MH⁺] 83

C53H97 N15O12 1135.74 Int 20 4-amino-2- (cyclopentylmethyl) butanoylpolymyxin [D- cyclohexylalanine- 6]nonapeptide 6.10 1137 [MH⁺] 84

C53H97 N15O13 1151.74 Example 48 (S)-4-amino-2- (cyclohexyl- methoxy)butanoyl L- Thr-L-Dap- polymyxin [D- cyclohexylalanine- 6]heptapeptide.6.12 1153 [MH⁺], 1265 [M + TFA]⁺ 85

C52H95 N15O12 1121.73 Int 19 4-amino-2- cyclohexylbutanoyl L-Thr-L-Dap-polymyxin [D- cyclohexylalanine- 6]heptapeptide. 6.09 1123 [MH⁺] 86

C53H97 N15O12 1135.74 Example 56 4-amino-3- cyclohexylbutanoyl polymyxin[D- cyclohexylalanine- 6]nonapeptide. Isomer 1 5.95 1137 [MH⁺] 87

C53H97 N15O12 1135.74 Example 57 4-amino-3- cyclohexylbutanoyl polymyxin[D- cyclohexylalanine- 6]nonapeptide. Isomer 2 6.04 1137 [MH⁺] 88

C56H97 N15O13 1187.74 Int 19 (S)-4-amino-2-((4- isopropylbenzyl)oxy)butanoyl L- Thr-L-Dap- polymyxin [D- cyclohexylalanine-6]heptapeptide 6.44 1189 [MH⁺] 89

C52H97 N15O12 1123.74 Int 20 2-(2-aminoethyl)- 5-methylhexanoylpolymyxin [D- cyclohexylalanine- 6]nonapeptide. Isomer 2 5.21 1125 [MH⁺]90

C55H95 N15O13 1173.72 Int 19 (S)-4-amino-2- ((3,5- dimethylbenzyl)oxy)butanoyl L- Thr-L-Dap- polymyxin [D- cyclohexylalanine-6]heptapeptide 5.63 1175 [MH⁺] 91

C54H99 N15O12 1149.76 Example 66 4-amino-3- (cyclohexylmethyl) butanoylpolymyxin [D- cyclohexylalanine- 6]nonapeptide. Isomer 1 6.05 1151 [MH⁺]92

C53H99 N15O12 1137.76 Int 20 2-(2-aminoethyl)- 4-ethylhexanoyl polymyxin[D- cyclohexylalanine]- 6 nonapeptide. Isomer 2 5.79 1139 [MH⁺] 93

C53H97 N15O12 1135.74 Tri-(N- Boc) Polymyxin B heptapeptide 4-amino-2-cyclohexylbutanoyl polymyxin L- alloThr-L-Dap- [D- cyclohexylalanine-6]-heptapeptide.

Additional compounds with modifications at position 6 and/or 7, ingeneral structure A, are shown in Table 1C:

TABLE 1C Further Additional Synthesis Examples R¹ Ex (N-terminal andside-chain on heptapeptide R² R³ Formula Mass Name 94

C52H89 N15O12 1115.7 4-amino-2- cyclohexylbutanoyl L-Thr-L-Dap-polymyxin[norleu- 7] heptapeptide. 95

C55H87 N15O12 1149.7 4-amino-2- cyclohexylbutanoyl L-Thr-L-Dap-polymyxin[Phe-7] heptapeptide 96

C54H91 N15O12 1141.7 4-amino-2- cyclohexylbutanoyl L-Thr-L-Dap-polymyxin[L- cyclohexylglycine- 7] heptapeptide 97

C53H97 N15O12 1135.7 4-amino-2- cyclohexylbutanoyl polymyxin E [L-cyclohexylalanine- 7] nonapeptide 98

C52H95 N15O12 1121.7 4-amino-2- cyclohexylbutanoyl polymyxin[D-cyclohexylglycine- 6] nonapeptide 99

C52H95 N15O12 1121.7 4-amino-2- cyclohexylbutanoyl L-Thr-L-Dab-polymyxin [D- cyclohexylalanine- 6], [norVal-7] heptapeptide

BIOLOGICAL ACTIVITY

To evaluate the potency and spectrum of the compounds, susceptibilitytesting was performed against up to nine strains of each of the Gramnegative pathogens, Escherichia coli, Pseudomonas aeruginosa, Klebsiellapneumoniae and Acinetobacter baumannii.

Comparator compounds C1 to C3 were also tested along with Polymyxin B.

Biological data is presented for examples and comparator compounds.

The values in Table 2 are MIC (μg/mL) against strains of E. Coll, K.pneumoniae, P. aeruginosa and A. baumanii, including strains which showelevated MICs to Polymyxin.

The data shows that the introduction of a halogen atom toD-phenylalanine at position 6 enhances activity against polymyxinresistant strains (see Example 2 compared with PMB).

The introduction of a lipophilic substituent to the phenyl group of theD-phenylalanine at position 6 significantly improves of activity againstresistant strains (see Example 4 and C1, and Example 5 and C2).

The modification of the N terminal group further improves the activityof the compounds against resistant strains (see Example 4 and Example 5compared to C3).

The authors have demonstrated a significant difference in activitybetween diastereomers in some examples where a compounds has beenprepared in two diastereomeric forms in the N-terminal group.

Additional compounds were prepared and the additional biological data ispresented in

Table 2A. The additional compounds were compared against PMB andcomparator compounds C4-C7. Comparator compounds C4-C6 are shown inTable 1A. Comparator compound C7 corresponds tooctanoyl-Dab-Thr-Dab-Cy[Dab-Dab-D-Phe-L-OctGly-Dab-Dab-Thr] reported asFADDI-002 by Velkov et al. (ACS Chemical Biology, 2014, 9, 1172).

The values in Table 2A are MIC (μg/mL).

Further the inventors have found that in order to provide a polymyxinderivative with a desirable combination of properties (activity againstpolymyxin-susceptible strains, activity against strains with reducedsusceptibility to polymyxins i.e. MIC≦4 μg/mL, cytotoxicity,pharmacokinetics, tissue distribution) it may be helpful to modify boththe polymyxin N-terminal group and the amino acid residues at position 6and/or position 7.

For a given N-terminal group, increasing the lipophilicity of theside-chains of the amino acid residues at position 6 and/or position 7improves the activity of a compound against strains with reducedsusceptibility to polymyxins (MIC≦4 μg/mL; so-called‘polymyxin-resistant strains’) as has been discussed above.

The substituents to the core of the molecule and at the N-terminusshould not be considered in isolation and the present inventors havefound that the combination of these groups both based on their specificgeometries as well as the overall lipophilicity of the molecule is veryimportant for the optimum biological properties.

The lipophilicity of a compound can be expressed as the logP where P isthe octanol:water partition coefficient. Methods of estimation of thisparameter are well known, and one such method of estimation uses thecalculated value A log P. The A Log P is a calculation of theGhose/Crippen group-contribution estimate for Log P, where P is therelative solubility of a compound in octanol versus water (Ghose, A. K.,Viswanadhan, V. N., and Wendoloski, “J. J., Prediction of Hydrophobic(Lipophilic) Properties of Small Organic Molecules Using FragmentMethods: An Analysis of A log P and C Log P Methods.” J. Phys. Chem. A,1998, 102, 3762-3772).

Velkov et al. have shown that providing highly lipophilic moieties asthe side-chains of the amino acid residues at position 6 and/or position7 in polymyxin decapeptides (with either the natural polymyxin acylchain or a suitable replacement acyl group at the N-terminus of adecapeptide) improves activity against resistant strains (see Velkov etal. ACS Chem Biol 9, 1172; 2014).

The present inventors have found that the activity of such compounds canbe further improved using the N-terminal groups described herein. Forexample, compound 26 shows further improved activity againstpolymyxin-resistant strains compared with C7, which is compound FADDI-02reported by Velkov et al. The biological activity of compound 26compared with C7 is reported in Table 2C. The values in Table 2C are MIC(μg/mL).

Thus derivatised polymyxin compounds can be provided with an optimumactivity against polymyxin-resistant strains where the combination ofN-terminal moieties and amino acid residues at position 6 and position 7is chosen to give an overall AlogP value greater (i.e. less negative)than −4.0, ideally greater than −3.5, such as between −3.0 and −2.0.

It can be seen that compounds such as 26 and C7 are less active againstpolymyxin-susceptible strains than compounds in a more negative A Log Prange. The present inventors have found that compounds having a A Log Pvalues lying in the range −5.0 to −6.3, such as within the range −5.5and −6.3, provided they have N-terminal groups with optimum geometry,can have excellent activity against both polymyxin-susceptible andresistant strains.

Compounds with A Log P in this region with appropriate N-terminalmoieties and amino acid moieties at position 6 and positon 7 can alsohave reduced cytotoxicity compared with polymyxin B.

If certain favourable moieties are present at the N terminal of thepolymyxin scaffold then the A Log P value may not fall into the optimumrange. Modulating lipophilicity by changing the side chains of aminoacids 6 and/or 7 may bring such compounds into the optimum range.

For example, Comparator compound C4 (A Log P 6.5) with a short alkylside chain has only moderate activity. This can be improved byincreasing the lipophilicity either at the N-terminus with C5 (A Log P5.5), or by increasing the lipophilicity of the side chain of amino acid6 by reduction to a cyclohexyl (see compound 40; A Log P 5.8). In someinstances increasing lipophilicity in the core (at the amino acidpositions 6 and/or 7) rather than the N-terminal moiety can lead toimproved biological properties e.g. compound 41 has significantly lowercytotoxicity compared with C6.

TABLE 2 E. coli K. pneumoniae P. aeruginosa A. baumanii ATCC ATCC ATCCATCC Ex. 058 059 060 061 25922 062 063 064 065 066 067 4352 068 07027853 053 056 BAA-747 PMB 4 4 4 16 0.25 128 32 8 4 8 128 0.25 8 32 0.5128 32 0.25 C1 1 2 1 2 0.03 32 8 2 2 1 64 0.03 2 4 0.25 16 1 0.06 C2 816 8 32 0.25 ND 128 32 16 32 >256 0.125 32 ND 0.5 >256 256 0.25 C3 2 1 48 0.5 32 8 4 0.5 4 32 0.5 2 4 1 16 16 1 1 ND ND 8 32 1 >64 >64 32 ND32 >32 1 32 >32 1 >32 >32 1 2 2 1 2 4 2 8 16 2 0.5 4 16 1 2 4 1 16 4 2 38 8 16 32 0.5 >64 >64 32 32 ND >64 0.5 4 4 1 64 4 2 4 0.5 0.5 0.5 2 0.5ND 4 2 1 1 8 0.5 1 2 1 2 0.5 0.5 5 1 1 2 8 0.06 ND 16 4 0.5 8 32 0.25 48 0.5 32 4 0.125 6 1 0.5 1 2 1 4 4 2 1 0.5 4 1 2 2 ND 8 4 1 7 2 1 4 8 116 32 8 1 4 32 1 2 2 ND 8 4 1 8 2 1 2 4 1 4 ND 1 1 0.5 8 1 2 2 1 4 2 1 92 2 4 8 1 64 >64 64 8 32 >64 0.5 2 2 1 64 32 1 10 1 1 2 2 2 2 8 2 1 4 41 2 2 2 4 4 1 11 16 32 16 64 1 >64 >64 >64 64 >64 >64 1 8 16 1 >64 32 212 0.25 1 1 1 0.125 8 4 1 0.5 1 8 0.125 1 1 0.25 8 ND 0.125 13 32 3232 >64 1 >64 >64 >64 >64 >64 >64 0.5 32 64 0.5 >64 >64 >8 14 4 8 8 160.25 8 64 8 8 8 >64 0.25 8 16 0.5 32 16 0.125 15 32 16 32 641 >64 >64 >64 64 64 >64 0.5 16 32 1 >64 >64 8 16 4 1 5 16 0.25 4 16 2 14 32 0.5 4 8 0.5 16 4 0.25 17 2 2 2 2 2 4 16 8 4 ND 32 2 4 4 2 2 2 2 182 1 2 2 2 2 4 4 2 2 4 2 4 4 2 2 2 2 19 16 ND ND ND 1 ND ND ND 16 ND ND 1ND ND 2 ND ND 1 20 4 ND ND ND 1 ND ND ND 1 ND ND 0.5 ND ND 1 ND ND 0.521 8 16 8 32 0.25 16 64 8 ND 16 >64 0.25 32 32 0.5 >64 64 0.5 22 2 2 4 80.5 16 32 4 1 4 64 0.5 4 4 1 64 32 0.5 23 2 2 2 2 2 4 8 4 2 2 4 1 4 4 22 1 2

TABLE 2A Additional Microbial Activity E. coli K. pneumoniae P.aeruginosa A. baumanii ATCC NCTC ATCC ATCC CCUG ATCC NCTC ATCC Ex. 058061 25922 9001 063 065 4352 13882 59347 068 070 27853 13424 053 056BAA-747 PMB 4 16 0.25 0.125 32 4 0.25 0.25 0.5 8 32 0.5 0.25 >64 32 0.25C4 >64 ND 1.0 ND ND >64 0.25 1 2 ND ND 1 0.5 ND ND 1 C5 2 16 0.06 0.03 81 0.06 0.125 0.5 8 32 0.125 0.25 >64 16 0.125 C6 1 8 0.125 0.06 8 0.250.06 0.125 0.125 2 8 0.125 0.03 32 32 0.06 C7 2 ND 1 ND ND 2 ND 1 2 NDND 0.5 1 ND ND 1 24 4 16 0.125 ND 64 8 0.125 ND 0.5 32 >64 0.250.25 >64 >64 0.25 25 1 0.5 0.5 ND 2 1 0.25 ND 2 1 1 1 0.5 ND ND 0.5 26 24 1 1 4 1 1 2 2 4 4 2 1 4 2 2 27 2 8 0.5 0.5 8 0.5 0.25 ND 1 4 2 0.50.25 8 4 0.5 28 1 8 0.25 0.125 8 1 0.125 ND 0.5 4 4 0.25 0.125 16 4 0.0629 32 ND 2 ND ND >64 ND ND 8 ND ND 4 4 ND ND 4 30 1 2 1 ND 4 1 1 1 2 2 21 2 4 2 1 31 2 16 0.5 ND 16 1 ND 0.5 1 2 2 0.5 0.5 32 16 0.25 32 2 160.25 0.125 16 ND 0.06 0.25 0.5 4 4 0.5 0.06 ND 64 0.25 33 2 16 0.250.125 64 2 0.03 0.5 0.5 8 8 0.25 0.125 64 32 0.25 34 2 16 0.25 0.125 324 0.125 0.125 0.25 4 4 0.25 0.06 32 16 0.125 35 4 16 0.25 0.06 16 0.50.125 0.06 0.25 1 2 0.25 0.25 >64 64 0.5 36 8 ND 0.125 ND ND 2 ND 0.1250.5 ND ND 0.5 2 ND ND 1 37 8 ND 0.06 0.06 ND 16 ND 0.25 0.5 ND ND 0.50.5 ND ND 0.125 38 2 16 0.06 0.06 32 1 ND 0.125 0.25 4 4 0.25 0.03 32 80.06 39 4 32 0.125 0.06 64 4 ND 0.125 0.5 4 4 0.5 0.03 32 64 0.06 40 816 0.125 0.03 16 2 ND 0.25 0.5 4 8 0.5 0.125 >64 64 0.06 41 4 8 0.1250.06 16 1.5 ND 0.125 0.5 4 4 0.5 0.06 >32 32 0.06 42 4 8 0.5 0.06 32 2ND 0.25 0.5 2 4 0.5 0.125 >64 32 0.125 43 1 8 0.25 0.06 16 0.5 ND 0.250.25 2 2 0.25 0.25 64 32 0.125 44 2 8 0.25 0.03 16 0.5 0.125 0.25 0.5 21 0.25 0.06 ND 8 0.06 45 4 16 0.25 0.06 16 1 ND 0.25 0.25 1 1 0.125 0.2564 64 0.25 46 8 ND 0.125 ND >64 2 ND 0.25 0.5 16 32 0.5 0.125 >64 >640.125 47 4 ND 0.25 0.125 ND 0.5 ND 0.5 0.5 ND ND 0.5 0.25 ND ND 0.125 484 32 0.125 ND 64 5 ND 0.125 0.25 8 16 0.25 0.25 >64 32 0.125 49 2 16 0.50.125 32 2 ND 0.5 0.25 2 2 0.25 0.25 64 64 0.5 50 2 16 0.5 ND ND 1 ND0.25 0.5 1 2 0.25 0.25 32 16 0.125 51 2 ND 0.5 ND ND 0.25 ND 0.5 0.5 NDND 0.5 0.25 ND ND 0.5 52 8 16 0.25 ND 64 8 ND 0.25 1 16 16 0.50.25 >64 >64 0.25 53 4 32 0.25 0.125 64 4 ND 0.25 0.5 8 8 0.25 0.5 64 640.5 54 4 16 0.125 0.06 32 1 ND 0.25 0.5 4 4 0.25 0.25 32 8 0.125 55 2 160.25 0.06 16 1 ND 0.25 0.5 4 4 0.125 0.25 8 4 0.125 56 16 ND 0.25 ND ND16 ND 0.25 0.5 ND ND 0.25 0.125 ND ND 0.125 57 16 ND 0.25 ND ND 8 ND0.25 0.5 ND ND 0.25 1 ND ND 1 58 4 16 0.25 0.125 64 4 ND 0.25 0.25 2 80.25 0.125 64 64 0.03 59 2 ND 0.125 0.06 32 2 0.125 0.25 0.25 4 8 0.250.06 32 16 0.03 60 16 ND 0.5 ND ND ND ND 0.5 1 ND ND ND 1 ND ND 0.5 61 8ND 0.25 ND ND 32 ND 0.25 0.5 ND ND 0.25 0.25 ND ND 0.25 62 4 32 0.125 ND64 8 ND 0.125 0.5 8 16 0.5 0.5 >64 >64 0.5 63 4 16 0.25 ND >64 4 ND0.125 0.5 8 8 0.25 0.125 64 32 0.125 64 8 32 0.125 ND 64 4 ND 0.25 0.258 16 0.25 0.25 32 32 0.125 65 4 16 0.25 ND 16 2 ND 0.25 0.5 2 2 0.51 >64 >64 0.25 66 8 32 0.125 ND 64 4 ND 0.125 0.5 8 32 0.25 0.06 >64 640.125 67 4 16 0.125 0.06 32 1 ND 0.25 0.25 8 16 0.25 0.25 64 16 0.25 682 16 0.125 ND 16 1 ND 0.25 0.5 1 1 0.25 0.25 >64 64 0.25 69 4 16 0.060.03 16 0.5 0.25 0.25 0.5 4 8 0.25 0.06 >64 64 0.25 70 8 32 0.125 ND 648 ND 0.125 0.5 8 32 0.25 0.25 32 16 0.25 71 4 16 0.125 0.125 64 4 0.250.25 0.25 8 16 0.25 0.125 64 32 0.125 72 2 8 0.25 0.25 8 0.5 ND 0.25 0.54 8 0.25 0.125 64 16 0.25 73 1 2 0.125 0.125 8 2 ND 0.25 0.5 1 1 0.50.125 64 16 0.25 74 2 16 0.125 ND 16 2 ND 0.25 0.25 4 4 0.25 0.125 32 320.125 75 2 16 0.125 ND 16 1 ND 0.125 0.25 2 2 0.25 0.125 >64 64 0.125 768 ND 0.125 ND ND ND ND 0.25 0.5 ND ND 0.5 0.5 ND ND 0.5 77 8 ND 0.25 NDND 8 ND 0.5 0.5 ND ND 0.5 0.5 ND ND 1 78 4 ND 0.25 ND ND ND ND 0.25 0.25ND ND 0.25 0.06 ND ND 0.25 79 2 ND 0.5 ND ND 2 ND 0.5 0.5 ND ND 0.5 0.25ND ND 0.25

TABLE 2A-CONT. Further Additional Microbial Activity A. baumanii E. coliK. pneumoniae P. aeruginosa ATCC ATCC NCTC ATCC ATCC CCUG ATCC NCTC BAA-Ex. 058 061 25922 9001 063 065 4352 13882 59347 068 070 27853 13424 053056 747 80 2 8 0.125 0.03 8 2 0.06 0.25 0.5 2 2 0.25 0.125 64 32 0.12581 1 16 0.125 0.03 16 4 0.25 0.125 0.25 2 2 0.125 0.125 32 8 0.125 82 28 0.06 0.015 32 2 ND 0.125 0.125 4 8 0.125 0.03 64 16 0.125 83 4 16 0.50.06 16 1 ND 0.25 0.25 2 8 0.25 0.06 >64 64 0.125 84 8 8 0.125 ND 32 4ND 0.25 0.5 ND 8 0.25 0.25 >32 32 0.25 85 4 16 0.125 0.06 8 0.5 ND 0.50.5 2 4 0.5 0.125 64 64 0.125 86 8 32 0.125 0.06 >64 8 ND 0.5 0.5 ND 80.25 0.125 >64 64 0.125 87 4 16 0.125 0.125 16 0.5 ND 0.25 0.5 2 8 0.250.125 64 64 0.25 88 2 16 0.25 0.25 64 0.5 ND 0.25 0.5 4 4 0.25 0.125 6432 0.25 89 16 ND 0.125 ND ND 32 ND 0.25 1 ND ND 0.5 0.25 ND ND 0.5 90 216 0.125 0.125 64 4 ND 0.25 0.25 4 16 0.125 0.06 >64 32 0.125 91 4 ND0.125 ND ND 4 ND 0.25 0.5 ND ND 0.25 0.125 ND ND 0.25 92 4 ND 0.06 ND ND8 ND 0.25 1 ND ND 0.25 0.125 ND ND 0.125

The lipophilicity of the test compounds was estimated using thecalculated value A log P, as described above. The A log P values aregiven in Table 2B.

HK-2 cell IC₅₀ values were determined as described herein, and arereported in Table 2B. Values are reported relative to Polymyxin B.

TABLE 2B AlogP and IC₅₀ values HK-2 IC₅₀ Example AlogP (μg/mL) PMB −6.312 C1 −6.2 161 C2 −7.2 316 C3 −4.7 3 C4 −6.5 ND C5 −5.5 29 C6 −5.6 51 C7−4.5 ND 1 −5.9 7 2 −5.5 ND 3 −4.7 34 4 −4.7 32 5 −5.7 36 6 −3.7 3 7 −3.1ND 8 −3.1 3 9 −3.1 ND 10 −3.1 4 11 −5.5 ND 12 −5.5 54 13 −6.3 ND 14 −6.376 15 −5.5 ND 16 −5.5 32 17 −3.0 ND 18 −3.0 ND 19 −4.6 ND 20 −4.6 10 21−6.3 83 22 −5.6 17 23 −2.6 ND 24 −6.4 ND 25 −4.6 20 26 −2.7 2 27 −4.9 1828 −5.8 86 29 −5.9 ND 30 −3.7 4 31 −5.4 ND 32 −5.8 73 33 −5.8 75 34 −6.099 35 −5.7 152 36 −5.7 ND 37 −7.1 ND 38 −6.2 255 39 −6.3 337 40 −5.8 ND41 −5.8 206 42 −5.7 ND 43 −5.7 ND 44 −6.0 ND 45 −5.5 ND 46 −6.8 ND 47−5.6 ND 48 −6.6 ND 49 −6.2 ND 50 −5.7 ND 51 −5.7 ND 52 −6.5 ND 53 −6.0ND 54 −5.9 ND 55 −5.5 ND 56 −6.3 ND 57 −6.3 ND 58 −5.9 ND 59 −5.9 ND 60−6.1 ND 61 −6.1 ND 62 −5.8 ND 63 −5.5 ND 64 −6.1 ND 65 −5.5 ND 66 −5.8ND 67 −5.8 60 68 −6.1 ND 69 −5.4 ND 70 −6.2 ND 71 −6.1 ND 72 −5.1 ND 73−5.5 ND 74 −5.9 52 75 −5.5 ND 76 −5.5 ND 77 −5.5 ND 78 −6.2 ND 79 −5.5ND Example AlogP 80 −5.6 81 −6.0 82 −5.9 83 −5.4 84 −6.0 85 −5.5 86 −5.687 −5.6 88 −5.4 89 −5.5 90 −5.6 91 −5.1 92 −5.1

The in vitro activity of compounds 26 and C7 (FADDI-02) againstresistant bacterial strains was compared. The resistant strains includedincluding Escherichia coli, Pseudomonas aeruginosa, Klebsiellapneumoniae and Acinetobacter baumannii strains. The data is provided inTable 2C, where the strains are identified. The values in Table 2 areMIC (μg/mL).

TABLE 2C Comparison of in vitro activity between compounds 26, C7 andPMB Strain 26 C7 (FADDI-02) PMB E. coli CA059 1 2 4 CA060 1 2 4 CA061 24 16 K. pneumoniae CA062 2 16 64 CA063 2 8 32 CA064 2 4 8 CA066 1 2 8CA067 2 64 >64 N655 2 8 32 P. aeruginosa CA068 2 4 8 CA070 2 2 32 A.baumannii CA053 2 4 >64 CA056 2 4 32

Further Definitions

The compounds of formula (I), and optionally the compounds of formula(II) also, have an N terminal group —X—R^(T).

The group —R^(T) may be a group —R⁵ as described in WO 2013/072695, agroup —R⁵ as described in PCT/GB2014/051547 (WO 2014/188178) or a group—R¹⁵ as described in GB 1404301.2, and WO 2015/135976.

The examples of GB 1404301.2 and WO 2015/135976 describe the preparationof polymyxin compounds having modified N terminals. For each of thecompounds described and tested, the amino acid residues at positions 6and 7 were not modified, thus an L-phenylalanine residue (polymyxin B)or an L-leucine residue (colistin) is present at position 6 and anL-leucine residue is present at position 7.

These examples show that modification to the N terminal group may bemade without limiting biological activity. Further, those examples showthat changes to the N terminal group may improve biological activitywith respect to Polymyxin B. The modification of the N terminal groupmay also be associated with a reduction in toxicity, especially areduction in nephrotoxicity.

The worked examples in the present show that these N terminal group maybe used within compounds that are variant at position 6 and/or 7 withoutloss in biological activity. Indeed, in some instances the changes atthe 6 and/or 7 position may provide compounds having improved biologicalactivity.

Additional Preferences

The comments below are preferences for the terminal group —R^(T) takinginto account the terminal groups described in PCT/GB2014/051547 (nowpublished as WO 2014/188178) and GB 1404301.2, and additionally oralternatively WO 2015/135976.

-Q-

In one embodiment, -Q- is a covalent bond.

In one embodiment, -Q- is —CH(R^(B))—. In this embodiment, —R^(B) may bea group -L^(A)-R^(BB), or —R^(B) together with —R¹⁷ may form a 5- to10-membered nitrogen-containing monocyclic or bicyclic heterocycle, asdescribed in further detail below.

Where —R¹⁷ and —R^(A) together form a nitrogen-containing heterocycle,the group -Q- is preferably a covalent bond.

In one embodiment, -Q- is —CH(R^(B))—, and forms part of anitrogen-containing heterocycle. In this embodiment, —R^(B) may behydrogen.

Nitrogen—Containing Heterocycle

The groups —R¹⁷ and —R^(A) may, together with the carbon atoms to whichthey are attached, form a nitrogen-containing heterocycle. Similarly,—R¹⁷ and —R^(B) may, together with the carbon atoms to which they areattached, form a nitrogen-containing heterocycle. The nitrogen in thenitrogen-containing heterocycle refers to the nitrogen atom in —N(R¹⁶)—.

The nitrogen-containing heterocycle may be a monocyclic or bicyclicnitrogen-containing heterocycle. A bicyclic nitrogen-containingheterocycle has two fused rings. The nitrogen-containing heterocyclecontains a total of 5 to 10 ring atoms. Where the nitrogen-containingheterocycle is monocyclic it may have 5 to 7 ring atoms, for example 5to 6, such as 6, ring atoms. Where the nitrogen-containing heterocycleis bicyclic it may have 8 to 10 ring atoms, such as 9 to 10, such as 10,ring atoms. Each ring in the bicyclic heterocycle may have 5 to 7 ringatoms, for example 5 or 6, such as 6, ring atoms.

Where the nitrogen-containing heterocycle is bicyclic, one ring may bearomatic or partially unsaturated. The ring that is formed together withthe carbon atoms α and β to the group —X— (the first ring) is notaromatic. It is the second ring, which is the ring fused to the first,that may be aromatic. The first ring is saturated, except for the carbonring atoms that are shared with the second ring (bridge atoms), whichmay be may be part of the aromatic ring system of the second ring, forexample.

Where the nitrogen-containing heterocycle is monocyclic, each carbonring atom in —R¹⁷ and —R^(A) or each carbon ring atom in —R¹⁷ and —R^(B)is optionally mono- or di-substituted with —R^(C).

Where the nitrogen-containing heterocycle is bicyclic, each carbon ringatom in —R¹⁷ and —R^(A) or each carbon ring atom in —R¹⁷ and —R^(B) isoptionally mono- or di-substituted with —R^(D), as appropriate. A carbonring atom may be unsubstituted or mono-substituted with —R^(D) if thatcarbon ring atom is part of an aromatic ring system, or is part of anunsaturated bond.

The group —R^(D) includes the group —R^(C). In one embodiment, where thenitrogen-containing heterocycle is bicyclic, each carbon ring atom inthe second ring is optionally mono-or di-substituted with —R^(C) andeach carbon ring atom in the first ring in is optionally mono-ordi-substituted with —R^(C).

In one embodiment, the nitrogen-containing heterocycle is a monocyclicnitrogen-containing heterocycle.

In one embodiment, the nitrogen-containing heterocycle is a bicyclicnitrogen-containing heterocycle.

In one embodiment, one carbon ring atom in the nitrogen-containingheterocycle is mono- or di-substituted, such as mono-substituted, with—R^(C) or substituted with -L^(B)-R^(BB), where present, for examplemono-substituted with —R^(C). In one embodiment, one carbon ring atom in—R¹⁷ and —R^(A) or —R¹⁷ and —R^(B) is mono- or di-substituted, such asmono-substituted, with —R^(C), for example -L^(A)-R^(CC). In theseembodiments, the remaining carbon atoms in the nitrogen-containingheterocycle are unsubstituted. This embodiment is preferred when thenitrogen-containing heterocycle is monocyclic.

Where the nitrogen-containing heterocycle is bicyclic, each carbon ringatom in the nitrogen-containing heterocycle may be unsubstituted.Alternatively, where the nitrogen heterocycle is bicyclic one carbonring atom in the nitrogen-containing heterocycle may be mono- ordi-substituted, such as mono-substituted, with —R^(C) or -L^(B)-R^(BB),such as with —R^(C). For example, where the nitrogen heterocycle isbicyclic one carbon ring atom in —R¹⁷ and —R^(A) or —R¹⁷ and —R^(B) ismono- or di- substituted, such as mono-substituted, with —R^(C), forexample -L^(A)-R^(CC). In these embodiments, the remaining carbon atomsin the nitrogen-containing heterocycle are unsubstituted.

The nitrogen-containing heterocycle may contain further hetero ringatoms independently selected from nitrogen, oxygen and sulfur. Where thenitrogen-containing heterocycle is a monocyclic, the heterocycleoptionally contains one further nitrogen, oxygen or sulfur ring atom.Where the nitrogen-containing heterocycle is a bicyclicnitrogen-containing heterocycle, the heterocycle optionally containsone, two or three further heteroatoms, where each heteroatom isindependently selected from the group consisting of nitrogen, oxygen andsulfur. In a bicyclic system, the further heteroatoms atoms may beprovided in the first or second rings, such as the first ring.

In one embodiment, where a further heteroatom is provided, thatheteroatom is nitrogen. In one embodiment, one further heteroatom isprovided, such as one further nitrogen heteroatom.

In one embodiment, the nitrogen-containing heterocycle does not containa further heteroatom.

Where two heteroatoms are provided in a ring, they are not separated byan unsubstituted methylene group (—CH₂—) or a mono-substituted methylenegroup (e.g. —CH(R^(C))—), and optionally they are not separated by adi-substituted methylene group (e.g. —C(R^(C))₂—).

Where reference is made to a further nitrogen ring atom, the ring atommay be provided as a group —NH—, and the nitrogen atom may be optionallysubstituted with —R^(N) or —R^(NA), as appropriate. A further nitrogenring atom may be unsubstituted if it is part of an aromatic ring system,or is part of an unsaturated bond.

Where reference is made to a further sulfur ring atom, the sulfur ringatom may be provided as —S—, —S(O)— or —S(O)₂—, such as —S—.

Each further nitrogen ring atom is optionally substituted with a group—R^(N), as appropriate, with the exception of a further nitrogen ringatom that is connected to the carbon that is α to the group —X—, whichnitrogen ring atom is optionally substituted with —R^(NA). This is shownschematically below for two exemplary R¹⁵—X— groups comprisingmonocyclic heterocycles containing a further nitrogen ring atom:

-   -   where the ring system on the right has a nitrogen ring atom that        is connected to the carbon atom that is a to the group —X—. Such        a nitrogen atom is optionally substituted with —R^(NA), and is        shown substituted with —R^(NA). The ring system on the left has        a nitrogen ring atom that is not connected to the carbon atom        that is a to the group —X— (it is attached to a carbon β to the        group —X—). Such a nitrogen atom is optionally substituted with        —R^(N), and is shown substituted with —R^(N). In the exemplary        ring structures shown above the carbon ring atoms are shown to        be unsubstituted. As described herein, carbon ring atoms that        are present in —R¹⁷ and —R^(A) are optionally mono- or        di-substituted.

It is noted that the definitions for —R^(NA) do not encompass groupsthat would together with the further nitrogen ring atom form an amidegroup.

When a second ring is present and that second ring is an aromatic ringcontaining one or more further nitrogen atoms, a nitrogen atom in thearomatic ring may not be substituted with a group —R^(N), asappropriate.

Where a further nitrogen ring atom is substituted with —R^(N) or—R^(NA), as appropriate, each carbon ring atom in thenitrogen-containing heterocycle may be unsubstituted.

Where —R¹⁷ and —R^(A) together form a monocyclic nitrogen-containingheterocycle, the heterocycle is substituted with at least one groupselected from —R^(C), and —R^(N), —R^(NA) and -L^(B)-R^(BB) i.e. atleast one of these groups must be present as a ring substituent at theappropriate position. Thus, in this embodiment, where thenitrogen-containing heterocycle is monocyclic and does not contain afurther nitrogen atom, at least one carbon ring atom must be substitutedwith —R^(C) or -L^(B)-R^(BB), where present. Further, in thisembodiment, where the nitrogen-containing heterocycle is monocyclic andcontains a further nitrogen atom, and that nitrogen atom isunsubstituted, at least one carbon ring atom must be substituted with—R^(C) or -L^(B)-R^(BB), where present. If a further nitrogen atom inthe monocyclic nitrogen-containing heterocycle is substituted with agroup —R^(N) or —R^(NA), the carbon ring atoms may be unsubstituted oroptionally mono- or di-substituted.

Where —R¹⁷ and —R^(B) together form a monocyclic nitrogen-containingheterocycle, the heterocycle is substituted with at least one groupselected from —R^(C), and —R^(N), where present. Alternatively theheterocycle is optionally substituted if —R^(A) is -L^(A)-R^(AA). In oneembodiment, the monocyclic nitrogen-containing heterocycle isunsubstituted when the group —R^(A) is -L^(A)-R^(AA).

If —R^(A) is hydrogen, the monocyclic nitrogen-containing heterocyclemust be substituted with at least one group selected from —R^(C), and—R^(N), where present. Here, if the nitrogen-containing heterocycle ismonocyclic and does not contain a further nitrogen atom, at least onecarbon ring atom must be substituted with —R^(C). Further, in thisembodiment, where the nitrogen-containing heterocycle is monocyclic andcontains a further nitrogen atom, and that nitrogen atom isunsubstituted, at least one carbon ring atom must be substituted with—R^(C). If a further nitrogen atom in the monocyclic nitrogen-containingheterocycle is substituted with a group —R^(N), the carbon ring atomsmay be unsubstituted or optionally mono- or di-substituted.

Where a nitrogen-containing heterocycle is bicyclic, each furthernitrogen ring atom may be unsubstituted. Alternatively, where thenitrogen heterocycle is bicyclic one further nitrogen ring atom may besubstituted with a group —R^(N), except where the further nitrogen ringatom is connected to the carbon that is a to the group —X—, that furthernitrogen ring atom is substituted with a group —R^(NA).

In one embodiment, a monocyclic nitrogen-containing heterocycle ismono-substituted with —R^(C). Thus, one carbon ring atom in the group—R¹⁷ and —R^(A) or —R¹⁷ and —R^(B) is mono-substituted with —R^(C).

In one embodiment, a monocyclic nitrogen-containing heterocyclecontaining a further nitrogen ring atom is mono-substituted with a group—R^(C), —R^(N) or —R^(NA), for example mono-substituted with a group—R^(N) or —R^(NA) or mono-substituted with a group —R^(C). Thus, onering atom in the group —R¹⁷ and —R^(A) or —R¹⁷ and —R^(B) ismono-substituted.

The nitrogen-containing heterocycle may be selected from the groupconsisting of pyrrolidine, piperidine, piperazine, 1,4-diazepine,indoline, 1,2,3,4-tetrahydroquinoline, 1,2,3,4-tetrahydroisoquinoline,1,2,3,4-tetrahydroquinoxaline,1,2,3,4,6,7,8,8a-octahydropyrrolo[1,2-a]pyrazine,1,2,3,4-tetrahydropyrrolo[1,2-a]pyrazine,5,6,7,8-tetrahydro-1,6-naphthyridine and1,2,3,4-tetrahydro-2,6-naphthyridine. In the bicyclic systems thearomatic ring, where present, is provided as the second ring.

The monocyclic nitrogen-containing heterocycles pyrrolidine, piperidine,piperazine, and 1,4-diazepine are substituted as discussed above.

The bicyclic nitrogen-containing heterocycles indoline,1,2,3,4-tetrahydroquinoline, 1,2,3,4-tetrahydroisoquinoline and1,2,3,4-tetrahydroquinoxaline may be substituted or unsubstituted, asdiscussed above.

A nitrogen-containing heterocycle may be selected from the groupconsisting of pyrrolidine, piperidine, piperazine, and 1,4-diazepine.

In one embodiment, a nitrogen-containing heterocycle is selected frompyrrolidine, piperidine and piperazine.

In one embodiment, a bicyclic nitrogen-containing heterocycle has afirst ring selected from pyrrolidine, piperidine and piperazine fused toa second ring, which may be an aromatic ring. Examples of the secondring include cyclohexane, benzene and pyridine ring

In one embodiment, the groups —R¹⁷ and —R^(A) together form a nitrogenheterocycle when -Q- is a covalent bond. Here, the group —NR¹⁶— islocated on a carbon atom that is β to the group —X—.

In another embodiment, the groups —R¹⁷ and —R^(A) together form anitrogen heterocycle when -Q- is not a covalent bond. Here, the group—NR¹⁶— is located on a carbon atom that is γ to the group —X—.

In one embodiment, —R¹⁷ and —R^(A) are selected from*—CH(R^(C1))CH(R^(C1))CH(R^(C1))—, *—CH(R^(C1))CH(R^(C1))—, and*—N(R^(NA))CH(R^(C1))CH(R^(C1))— where * indicates the point ofattachment to the carbon α to the group —X—, —R^(C1) is hydrogen or—R^(C), and at least one carbon or nitrogen atom is substituted with—R^(C) or —R^(NA), as appropriate.

Exemplary nitrogen-containing heterocycle structures are given in the—R¹⁵ section below.

Carbocycle and Heterocycle

In one embodiment, —R^(A) and —R^(B) together form a 5- to 10-memberedcarbocycle or heterocycle. Here, -Q- is not a covalent bond. Thecarbocycle or heterocycle may be substituted or unsubstituted.

A carbocycle or a heterocycle may be monocyclic or bicyclic. A bicycliccarbocycle or a heterocycle has two fused rings.

The carbocycle or a heterocycle contains a total of 5 to 10 ring atoms.Where the carbocycle or heterocycle is monocyclic it may have 5 to 7ring atoms, for example 5 to 6, such as 6, ring atoms. Where thecarbocycle or heterocycle is bicyclic it may have 8 to 10 ring atoms,such as 9 to 10, such as 10, ring atoms. Each ring in the bicyclicsystem may have 5 to 7 ring atoms, for example 5 or 6, such as 6, ringatoms.

Where the carbocycle or heterocycle is bicyclic, one ring may bearomatic or partially unsaturated. The ring that is formed together withthe carbon atoms α and β to the group —X— (the first ring) is notaromatic. It is the second ring, which is the ring fused to the first,that may be aromatic. The first ring is saturated, except for the carbonring atoms that are shared with the second ring (bridge atoms), whichmay be may be part of the aromatic ring system of the second ring.

A bicyclic heterocycle is a heterocycle having a heteroatom, such as N,S, or O in either the first or second ring.

In one embodiment, a heteroatom is present in the first ring. In oneembodiment, a heteroatom is present in the second ring.

The heterocycle includes one or more heteroatoms independently selectedfrom N, S, and O. In one embodiment heterocycle includes one or two,such as one heteroatom.

In one embodiment, the heteroatom is nitrogen.

In one embodiment, one heteroatom present, such as one nitrogenheteroatom.

Where the carbocycle or a heterocycle is monocyclic, each carbon ringatom in —R^(A) and —R^(B) is optionally mono- or di-substituted with—R^(C).

Where the carbocycle or a heterocycle is bicyclic, each carbon ring atomin —R^(A) and —R^(B) is optionally mono- or di-substituted with —R^(D),which includes —R^(C).

Where reference is made to a nitrogen ring atom, the ring atom may beprovided as a group —NH—, and the nitrogen atom may be optionallysubstituted with —R^(N) or —R^(NA), as appropriate. A further nitrogenring atom may be unsubstituted if it is part of an aromatic ring system,or is part of an unsaturated bond.

Where reference is made to a sulfur ring atom in the heterocycle, thesulfur ring atom may be provided as —S—, —S(O)— or —S(O)₂—, such as —S—.

In one embodiment, one carbon ring atom in the carbocycle or heterocycleis mono- or di-substituted, such as mono-substituted, with —R^(C) or—R^(D), where appropriate. In this embodiment, the remaining carbonatoms in the carbocycle or heterocycle may be unsubstituted. Thisembodiment is preferred when the carbocycle or heterocycle ismonocyclic.

In one embodiment, the heterocycle has a nitrogen ring atom and thatatom is optionally substituted with —R^(N), with the exception of anitrogen ring atom that is connected to the carbon that is a to thegroup —X—, which nitrogen ring atom is optionally substituted with—R^(NA). In one embodiment, where a nitrogen ring atom is present in theheterocycle, that ring atom may be substituted. In this embodiment, theremaining carbon atoms in the carbocycle or heterocycle may beunsubstituted. This embodiment is preferred when the heterocycle ismonocyclic.

It is noted that the definitions for —R^(NA) do not encompass groupsthat would together with a nitrogen ring atom form an amide group.

When a second ring is present and that second ring is an aromatic ringcontaining one or more nitrogen atoms, a nitrogen atom in the aromaticring may be substituted with a group —R^(N), as appropriate.

In one embodiment, a monocyclic carbocycle is selected from cyclohexaneand cyclopentane, which may be substituted as discussed above.

In one embodiment, a monocyclic heterocycle is selected frompyrrolidine, tetrahydrofuran, tetrahydrothiophene, piperidine,piperazine, 1,4-dioxane, morpholine, thiomorpholine and 1,4-diazepine,which may be substituted as discussed above.

In one embodiment, a monocyclic carbocycle is selected from indane andtetralin.

In one embodiment, a bicyclic heterocycle is selected from indoline,1,2,3,4-tetrahydroquinoline, 1,2,3,4-tetrahydroisoquinoline,1,2,3,4-tetrahydroquinoxaline, chromane, and dihydrobenzofuran, whichmay be substituted as discussed above.

—R¹⁵

The group —R¹⁵ together with —X— may be regarded as an N terminalsubstituent group in the compounds of formula (III). —R¹⁵ contains anamino group which may be a group —NR¹⁶R¹⁷, or a group —NR¹⁶— where thenitrogen is present as a ring atom in a nitrogen-containing heterocycle.

In the compounds of the invention, the nitrogen group —NR¹⁶R¹⁷ must bebonded to one methylene group (i.e. a group —CH₂—). Thus, —R¹⁵ mustcontain a group —CH₂NR¹⁶R¹⁷.

When the nitrogen group —NR¹⁶— is provided in a nitrogen-containingheterocycle (i.e. —R¹⁷ and —R^(A) form a ring, or —R¹⁷ and —R^(B) form aring), the nitrogen atom must be bonded to one neighboring carbon atomthat is part of a methylene group. This is a requirement for the group—R¹⁵. However, the other neighboring ring carbon atom is not necessarilypart of a methylene group (it may be a methylene or methine group). Inone embodiment, the nitrogen atom in —NR¹⁶— is bonded to two ringmethylene groups (i.e. both neighboring ring carbon atoms are providedin methylene groups). In one embodiment, the nitrogen atom in —NR¹⁶— isbonded to a carbon ring atom that is part of a methylene group and acarbon ring atom that is part of a methylene or methine group.

In one embodiment, —R¹⁵ is selected from the groups listed below. Thegroups shown below include groups where —R¹⁷ and —R^(A) together form anitrogen-containing heterocycle.

In the embodiments below —R^(C1) is hydrogen or —R^(C); —R^(N1) ishydrogen or —R^(NA); —R^(D1) is hydrogen or —R^(D); —R^(A) is hydrogenor -L^(A)-R^(AA)—, —R^(B) is hydrogen or -L^(B)-R^(BB); and —R¹⁶ isindependently hydrogen or C₁₋₄ alkyl; —R¹⁷ is independently hydrogen orC₁₋₄ alkyl; or —NR¹⁶R¹⁷ is a guanidine group. As noted above, where -Q-is a covalent bond —R^(A) is -L^(A)-R^(AA), and where -Q- is —CH(R^(B))—one or both of —R^(A) and —R^(B) is not hydrogen. Where thenitrogen-containing heterocycle is monocyclic, it should be substitutedwith at least one group selected from —R^(C), and -L^(B)-R^(BB), —R^(NA)and —R^(N).

In one embodiment, —R¹⁵ is selected from the group consisting of:

In one embodiment, —R¹⁵ is selected from the group consisting of:

In one embodiment, —R¹⁵ is selected from the group consisting of:

In one embodiment, —R¹⁵ is selected from the group consisting of:

In one embodiment, —R¹⁵ is selected from the group consisting of:

In one embodiment, —R¹⁵ is selected from the group consisting of:

In one embodiment, —R¹⁵ is selected from the group consisting of:

In one embodiment, —R¹⁵ is selected from the group concisting of:

In one embodiment, —R¹⁵ is selected from the group consisting of:

In one embodiment, —R¹⁵ is selected from the group consisting of:

In one embodiment, —R¹⁵ is selected from the group consisting of:

In one embodiment, —R¹⁵ is selected from the group consisting of:

In one embodiment, —R¹⁵ is:

such as

In one embodiment, —R¹⁵ is:

such as

In one embodiment, —R¹⁵ is:

such as,

In one embodiment, —R¹⁵ is:

such as

In one embodiment, —R¹⁵ is:

such as

The structures shown above include examples where —R¹⁵ contains anitrogen-containing heterocycle. These are compounds where the groups—R¹⁷ and —R^(A), together with the carbon atoms to which they areattached, form a nitrogen heterocycle. The nitrogen heterocycles shownabove are monocyclic nitrogen heterocycles.

Each carbon ring atom in the group —R¹⁷ and —R^(A) may be substitutedwith —R^(C1). Where —R^(C1) is hydrogen, the carbon ring atom isunsubstituted.

A nitrogen ring atom in the group —R¹⁷ and —R^(A), where present, issubstituted with —R^(N1).

Where —R^(N1) is hydrogen, the nitrogen ring atom is unsubstituted.

Where the nitrogen-containing heterocycle contains a further nitrogenatom, it is preferred that the further nitrogen atom is substituted with—R^(N) or —R^(NA), as appropriate. In this embodiment, the ring carbonatoms may be unsubstituted. Where the nitrogen-containing heterocycledoes not contain a further nitrogen atom, one of the carbon ring atomsis substituted with —R^(C) or -L^(B)-R^(BB), and preferably one of thecarbon ring atoms group —R¹⁷ and —R^(A) is substituted with —R^(C).

The compounds of the invention also include compounds where —R¹⁷ and—R^(A), together with the carbon atoms to which they are attached, forma bicyclic nitrogen heterocycle. In this embodiment, it is not necessaryfor the carbon or nitrogen ring atoms in —R¹⁷ and —R^(A) to besubstituted (i.e. each of —R^(C) and —R^(N) may be hydrogen).

Additionally or alternatively to the —R¹⁵ groups shown above, —R¹⁵ isselected from:

Additionally or alternatively to the —R¹⁵ groups shown above, —R¹⁵ isselected from:

Additionally or alternatively to the —R¹⁵ groups shown above, in oneembodiment —R¹⁵ is selected from:

such as

In one embodiment, —R^(A) and —R^(B) may together form a carbocycle or aheterocycle. The ring atoms of the carbocycle or heterocycle may beoptionally substituted. A carbon ring atom may be optionally mono- ordi-substituted with —R^(C). A nitrogen ring atom, where present, may beoptionally substituted with —R^(N), except that a nitrogen ring atomthat is connected to the carbon that is a to the group —X— is optionallysubstituted with —R^(NA).

In the embodiments below —R^(C1) is hydrogen or —R^(C); —R^(N1) ishydrogen or —R^(NA); —R^(D1) is hydrogen or —R^(D); and —R¹⁶ isindependently hydrogen or C₁₋₄ alkyl; —R¹⁷ is independently hydrogen orC₁₋₄ alkyl; or —NR¹⁶R¹⁷ is a guanidine group. Where thenitrogen-containing carbocycle heterocycle is monocyclic, it isoptionally substituted with at least one group selected from —R^(C), and—R^(NA) and —R^(N).

Additionally or alternatively to the —R¹⁵ groups shown above, in oneembodiment —R¹⁵ is selected from:

Additionally or alternatively to the —R¹⁵ groups shown above, in oneembodiment —R¹⁵ is selected from:

—R^(A)

In one embodiment, —R^(A) is not hydrogen. In one embodiment, —R^(A) is-L^(A)-R^(AA). In one embodiment, —R^(A) is —R^(AA). In theseembodiments, —R^(B), if present, may be hydrogen.

In one embodiment, where —R^(A) is not hydrogen, for example where—R^(A) is -L^(A)-R^(AA) or —R^(A) and —R¹⁷ together form anitrogen-containing heterocycle, —R¹⁵ is an amino-containing group:

Where —R^(A) is -L^(A)-R^(AA) it is noted that this group does notencompass a substituent containing the group —C(O)N(R¹¹)—*, where theasterisk indicates the point of attachment to the carbon that is a tothe group —X—. The inventors have found that where the group—C(O)N(R¹¹)—* is present, biological activity is reduced.

In one embodiment, —R^(A) and —R¹⁷ together form a 5- to 10-memberednitrogen-containing monocyclic or bicyclic heterocycle.

In one embodiment, —R^(A) and —R^(B) together form a 5- to 10-memberedcarbocycle or heterocycle. Here, -Q- is not a covalent bond.

In one embodiment, —R^(A) is not —NHEt or —NEt₂, for example whereR¹⁵—X— is an N terminal substituent to Polymyxin B nonapeptide (PMBN).

In one embodiment, —R^(A) is not —NHR^(PA) or —N(R^(PA))₂, where each—R^(PA) is C₁₋₁₀ alkyl, such as C₈₋₁₀ alkyl, such as C₁₋₈ alkyl, such asC₁₋₄ alkyl, such as C₁₋₂ alkyl, for example where R¹⁵—X— is an Nterminal substituent to Polymyxin B nonapeptide (PMBN).

In one embodiment, —R^(A) is not a group having an oxygen atom attachedto the carbon that is α to the group —X—. In one embodiment, —R^(A) isnot a group having a nitrogen atom attached to the carbon that is a tothe group —X—. The definitions for the group -L^(A)-R^(AA) may beconstrued accordingly.

—R^(B)

In one embodiment, —R^(B), where present, is hydrogen. In oneembodiment, -Q- is a covalent bond and —R^(B) is accordingly absent.

In one embodiment, —R^(B) is -L^(A)-R^(BB). In one embodiment, —R^(B) is—R^(BB). In these embodiments, —R^(A) may be hydrogen.

In one embodiment, —R^(B) is not C₃₋₁₀ cycloalkyl, for example is notcyclohexyl.

In one embodiment, —R^(B) and —R¹⁷ together form a 5- to 10-memberednitrogen-containing monocyclic or bicyclic heterocycle.

In one embodiment, —R^(A) and —R^(B) together form a 5- to 10-memberedcarbocycle or heterocycle. Here, -Q- is not a covalent bond.

Where -Q- is present and is part of a nitrogen-containing heterocycleand —R^(B) is -L^(A)-R^(BB), the nitrogen-containing heterocycle isoptionally substituted. Thus each carbon ring atom in —R^(B) and —R¹⁷ isoptionally substituted with —R^(C), and each nitrogen ring atom in—R^(B) and —R¹⁷ is optionally substituted with —R^(N).

In one embodiment one of —R^(A) and —R^(B) is hydrogen. The other of—R^(A) and —R^(B) is therefore not hydrogen.

It is noted that the group -L^(B)-R^(BB) encompasses a substituentcontaining the group —C(O)N(R¹¹)—*, where the asterisk indicates thepoint of attachment to the carbon that is β to the group —X—.

—R^(C), —R^(N) and —R^(NA)

The groups —R^(A) and —R¹⁷ or —R^(B) and —R¹⁷ may together form a 5- to10-membered nitrogen-containing monocyclic or bicyclic heterocycle, and—R^(A) and —R^(B) may together form a 5- to 10-membered monocyclic orbicyclic carbocycle , or together form a 5- to 10-monocyclic or bicyclicheterocycle. The ring atoms that are present in the nitrogen-containingheterocycle and the carbocycle or heterocycle may be substituted orunsubstituted as described herein.

The nitrogen-containing heterocycle includes ring atoms that are part of—R^(A) and —R¹⁷ or —R^(B) and —R¹⁷. Where —R^(A) and —R¹⁷ or —R^(B) and—R¹⁷ form a nitrogen-containing monocyclic or bicyclic heterocycle, eachcarbon ring atom in the group —R^(A) and —R¹⁷ or the group —R^(B) and—R¹⁷ may be optionally substituted with —R^(C). These carbon ring atomsmay be mono- or di-substituted with —R^(C). In one embodiment, eachcarbon ring atom is optionally mono-substituted with —R^(C).

As described herein a nitrogen-containing monocyclic heterocycle must besubstituted. The substituent may be present as a substituent to a ringatom that is part of —R^(A) and —R¹⁷ or —R^(B) and —R¹⁷. Thus, a group—R^(C), —R^(N) or —R^(NA), where appropriate, is present. Alternativelythe substituent may be present at the carbon to the group —X— i.e.-L^(B)-R^(BB) is present.

The nitrogen-containing heterocycle may contain further nitrogen ringatoms. Each further nitrogen ring atom may be optionally substitutedwith —R^(N), as appropriate. However, where the further nitrogen atom isbonded to the carbon that is α to the group —X—, that ring nitrogen atomis optionally substituted with —R^(NA).

In one embodiment, —R^(A) and —R^(B) together form a 5- to 10-memberedmonocyclic or bicyclic carbocycle or heterocycle. In the monocycle, eachring carbon atom in —R^(A) and —R^(B) is optionally mono- ordi-substituted with —R^(C). These carbon ring atoms may be mono- ordi-substituted with —R^(C). In one embodiment, each carbon ring atom isoptionally mono- substituted with —R^(C). In the bicycle, each ringcarbon atom in —R^(A) and —R^(B) is optionally mono- or di-substitutedwith —R^(C). These carbon ring atoms may be mono- or di-substituted with—R^(D).

A 5- to 10-membered monocyclic or bicyclic heterocycle may contain anitrogen ring atom. Each nitrogen ring atom may be optionallysubstituted with —R^(N), as appropriate. However, where the furthernitrogen atom is bonded to the carbon that is a to the group —X—, thatring nitrogen atom is optionally substituted with —R^(NA).

One of the carbon ring atoms that is part of —R^(A) and —R¹⁷, —R^(B) and—R¹⁷, or —R^(A) and —R^(B) may be substituted with oxo (═O). A ringcarbon atom that is connected to the nitrogen atom in —N(R¹⁶)— is notsubstituted with oxo. Where such a carbon ring atom is substituted withoxo it may be joined to a further nitrogen ring atom (where such ispresent) to from an amide group. It is noted that a further nitrogenatom may be connected to the carbon atom that is α to the group —X—. Theinventors understand that where an amide group is present within anitrogen-containing heterocycle as a substituent to the carbon β to thegroup —X—, biological activity is not reduced.

In one embodiment, where a ring carbon atom is connected to a furthernitrogen ring atom that is connected to the carbon atom that is α to thegroup —X—, that ring carbon atom is not substituted with oxo.

Similarly, where such a carbon ring atom is substituted with oxo it maybe joined to a further oxygen ring atom (where such is present) and anester group may be formed.

In one embodiment, the nitrogen-containing heterocycle does not includea ring amide, carbamate, urea or ester group. In one embodiment, afurther nitrogen ring atom connected to the carbon that is α to thegroup —X— is not part of an amide, carbamate or urea group.

In one embodiment, a further oxygen ring atom connected to the carbonthat is α to the group —X— is not part of a carbamate or ester group.

Where —R¹⁷ and —R^(A) form a monocyclic nitrogen-containing heterocycle,one ring atom (formed together with the carbon atoms α and β to thegroup —X—) must be substituted. Here the monocyclic nitrogen heterocyclemust have a substituent group present on a carbon ring atom or furthernitrogen ring atom, where present. Thus at least one group —R^(C),—R^(N), —R^(NA) or -L^(B)-R^(BB) must be present as a substituent to thenitrogen-containing heterocycle. In one embodiment, at least one group—R^(C), —R^(N) and —R^(NA) must be present as a substituent to thenitrogen-containing heterocycle.

In one embodiment, where —R¹⁷ and —R^(A) form a monocyclicnitrogen-containing heterocycle, one or two ring atoms in —R¹⁷ and—R^(A) are substituted. The remaining ring atoms in —R¹⁷ and —R^(A) areunsubstituted. In one embodiment, one ring atom in —R¹⁷ and —R^(A) issubstituted.

In one embodiment, where R¹⁷ and —R^(A) form a monocyclicnitrogen-containing heterocycle, one carbon ring atom in —R¹⁷ and —R^(A)is substituted with —R^(C), and the remaining ring atom in —R¹⁷ and—R^(A) are unsubstituted.

In one embodiment, where R¹⁷ and —R^(A) form a monocyclicnitrogen-containing heterocycle, and the heterocycle has a furthernitrogen ring atom, the further nitrogen is substituted with —R^(N) or—R^(NA), as appropriate, and the remaining ring atoms in —R¹⁷ and —R^(A)are unsubstituted. In one embodiment, where R¹⁷ and —R^(A) form amonocyclic nitrogen-containing heterocycle, and the heterocycle has afurther nitrogen ring atom, one carbon ring atom in —R¹⁷ and —R^(A) issubstituted with —R^(C), and the remaining ring atoms in —R¹⁷ and —R^(A)are unsubstituted.

Where —R¹⁷ and —R^(B) form a monocyclic nitrogen heterocycle, the ringatoms in the ring (formed together with the carbon atom β to the group—X—) need not be substituted. If the group —R^(A) is hydrogen, themonocyclic nitrogen heterocycle must have a substituent group present ona carbon ring atom or further nitrogen ring atom, where present.However, if the group —R^(A) is not hydrogen, then the carbon ring atomsor further nitrogen ring atom, where present, need not be substituted.

In one embodiment, where —R¹⁷ and —R^(B) form a monocyclicnitrogen-containing heterocycle, one or two ring atoms in —R¹⁷ and—R^(B) are substituted. The remaining ring atoms in —R¹⁷ and —R^(B) areunsubstituted. In one embodiment, one ring atoms in —R¹⁷ and —R^(B) issubstituted. In these embodiments, —R^(A) may be hydrogen.

In one embodiment, where R¹⁷ and —R^(B) form a monocyclicnitrogen-containing heterocycle, one carbon ring atom in —R¹⁷ and —R^(B)is substituted with —R^(C), and the remaining ring atoms in —R¹⁷ and—R^(B) are unsubstituted.

In one embodiment, where R¹⁷ and —R^(B) form a monocyclicnitrogen-containing heterocycle, and the heterocycle has a furthernitrogen ring atom, the further nitrogen is substituted with —R^(N), andthe remaining ring atoms in —R¹⁷ and —R^(B) are unsubstituted.

In one embodiment, where R¹⁷ and —R^(B) form a monocyclicnitrogen-containing heterocycle, and the heterocycle has a furthernitrogen ring atom, one carbon ring atom in —R¹⁷ and —R^(B) issubstituted with —R^(C), and the remaining ring atoms in —R¹⁷ and —R^(B)are unsubstituted.

A bicyclic nitrogen-containing heterocycle may be unsubstituted. Herethe second fused ring may be regarded as a substituent to the firstring.

In one embodiment, where R¹⁷ and —R^(A) form a bicyclicnitrogen-containing heterocycle, one carbon ring atom in —R¹⁷ and —R^(A)is substituted with —R^(D), and the remaining ring atoms in —R¹⁷ and—R^(A) are unsubstituted.

In one embodiment, where R¹⁷ and —R^(A) form a bicyclicnitrogen-containing heterocycle, and the heterocycle has a furthernitrogen ring atom, the further nitrogen is substituted with —R^(N) or—R^(NA), as appropriate, and the remaining ring atoms in —R¹⁷ and —R^(A)are unsubstituted. In one embodiment, where R¹⁷ and —R^(A) form abicyclic nitrogen-containing heterocycle, and the heterocycle has afurther nitrogen ring atom, one carbon ring atom in —R¹⁷ and —R^(A) issubstituted with —R^(D), and the remaining ring atoms in —R¹⁷ and —R^(A)are unsubstituted.

In one embodiment, a group —R^(D) is —R^(C) when it is provided as asubstituent on the first ring of a bicyclic nitrogen-containingheterocycle.

—R^(D)

In one embodiment, each —R^(D) is independently selected from —R^(C),halo, —OH, and —NH₂.

In one embodiment, each —R^(D) is independently selected from —R^(C) andhalo.

In one embodiment, each —R^(D) is independently —R^(C).

In one embodiment, each —R^(D) is independently -L^(C)-R^(CC).

A bicyclic nitrogen-containing heterocycle contains a first ring and asecond ring. The first ring is the nitrogen heterocycle including thecarbon atom that is β to the group —X—. In one embodiment each carbonring atom in —R¹⁷ and —R^(A) that is part of the first ring isoptionally mono- or di-substituted with —R^(C).

The second ring is the ring fused to the first ring. Each carbon ringatom in —R¹⁷ and —R^(A) that is part of the second ring is optionallymono- or di-substituted with —R^(D).

-L^(A)-

The group -L^(A)- may be a covalent bond.

Alternatively -L^(A)- may be a linking group. An asterisk is used toindicate the point at which the group point of attachment of the group-L^(A) to —R^(AA). Thus, the remaining attachment point connects to thecarbon that is a to the group —X—.

It is noted that -L^(A)- is not a group —N(R¹¹)C(O)—* where the asteriskis the point of attachment to —R^(AA). The inventors have found thatsuch groups have a poor biological activity, as discussed above.

In one embodiment, the linking group is selected from —R^(L)—*,—O-L^(AA)-*, —N(R¹¹)-L^(AA)-*, and —C(O)-L^(AA)-*.

In one embodiment, the linking group is selected from —R^(L)-*,—O-L^(AA)-*, and —C(O)-L^(AA)-*.

In one embodiment, the linking group is selected from —R^(L)-*,—N(R¹¹)-L^(AA)-*, and —C(O)-L^(AA)-*.

In one embodiment, the linking group is selected from —R^(L)-* and—C(O)-L^(AA)-*.

In one embodiment, the linking group is selected from —R^(L)-*,—O-L^(AA)-*, and —N(R¹¹)-L^(AA)-*.

In one embodiment, the linking group is selected from —R^(L)-* and—O-L^(AA)-*.

In one embodiment, the linking group is —R^(L)-*.

-L^(B)-

The group -L^(B)- may be a covalent bond.

Alternatively -L^(B)- may be a linking group.

An asterisk is used to indicate the point at which the group point ofattachment of the group -L^(B)- to —R^(BB). Thus, the remainingattachment point connects to the carbon that is β to the group —X— (i.e.the carbon atom in —CH(R^(B))—).

In one embodiment, the linking group is selected from R^(L)-*,—O-L^(AA)-*, —OC(O)-L^(AA)-*, —N(R¹¹)-L^(AA)-*, —C(O)-L^(AA)-*, and—C(O)O-L^(AA)-*.

In one embodiment, the linking group is selected from —R^(L)-*,—O-L^(AA)-*, —N(R¹¹)-L^(AA)-*, —C(O)-L^(AA)-*, —C(O)O-L^(AA)-*, and—C(O)N(R¹¹)-L^(AA)-*.

In one embodiment, the linking group is selected from —R^(L)-*,—O-L^(AA)-*, —N(R¹¹)-L^(AA)-*, —C(O)-L^(AA)-*, and —C(O)O-L^(AA)-*.

In one embodiment, the linking group is selected from —R^(L)-*,—O-L^(AA)-*, and —N(R¹¹)-L^(AA)-*.

In one embodiment, the linking group is —R^(L)-*.

Additionally or alternatively, the linking group is selected from—N(R¹¹)S(O)-L^(AA)-* and —N(R¹¹)S(O)₂-L^(AA)-*.

In one embodiment, the linking group is —N(R¹¹)S(O)₂-L^(AA)-*.

In one embodiment, the linking group is —N(R¹¹)S(O)₂—*.

Additionally or alternatively, the linking group is selected from—S(O)N(R¹¹)-L^(AA)-*, and —S(O)₂N(R¹¹)-L^(AA)-*.

In one embodiment, the linking group is —S(O)N(R¹¹)-L^(AA)-*.

In one embodiment, the linking group is —S(O)₂N(R¹¹)-L^(AA)-*.

-L^(C)-

The group -L^(C)- may be a covalent bond.

Alternatively -L^(C)- may be a linking group.

An asterisk is used to indicate the point at which the group point ofattachment of the group -L^(C)—to —R^(CC). Thus, the remainingattachment point connects to the carbon ring atom.

In one embodiment, the linking group is selected from R^(L)-*,—O-L^(AA)-*, —OC(O)-L^(AA)-*, —N(R¹¹)—L^(AA)-*, —C(O)-L^(AA)-*, and—C(O)O-L^(AA)-*.

In one embodiment, the linking group is selected from —R^(L)-*,—O-L^(AA)-*, —N(R¹¹)-L^(AA)-*, —C(O)-L^(AA)-*, —C(O)O-L^(AA)-*, and—C(O)N(R¹¹)-L^(AA)-*.

In one embodiment, the linking group is selected from —R^(L)-*,—O-L^(AA)-*, —N(R¹¹)-L^(AA)-*, —C(O)-L^(AA)-*, and —C(O)O-L^(AA)-*.

In one embodiment, the linking group is selected from —R^(L)-*,—O-L^(AA)-*, and —N(R¹¹)-L^(AA)-*.

In one embodiment, the linking group is —R^(L)-*.

Additionally or alternatively, the linking group is selected from—N(R¹¹)S(O)-L^(AA)-* and —N(R¹¹)S(O)₂-L^(AA)-*.

In one embodiment, the linking group is —N(R¹¹)S(O)₂-L^(AA)-*.

In one embodiment, the linking group is —N(R¹¹)S(O)₂—*.

Additionally or alternatively, the linking group is selected from—S(O)N(R¹¹)-L^(AA)-*, and —S(O)₂N(R¹¹)-L^(AA)-*.

In one embodiment, the linking group is —S(O)N(R¹¹)-L^(AA)-*.

In one embodiment, the linking group is —S(O)₂N(R¹¹)-L^(AA)-*.

-L^(AA)-

In one embodiment, a group -L^(AA)- is independently a covalent bond.

In one embodiment, a group -L^(AA)- is independently —R^(L).

-L^(N)-

In one embodiment, a group -L^(N)- is independently a covalent bond.

In one embodiment, a group -L^(N)- is a linking group.

An asterisk is used to indicate the point of attachment of the group-L^(N)- to —R^(NN). Thus, the remaining attachment point connects to thenitrogen ring atom.

The linking group may be independently selected from —S(O)-L^(AA)-*,—S(O)₂-L^(AA)-*, —C(O)-L^(AA)-* and —C(O)N(R¹¹)-L^(AA)-*. Thus, thelinking groups may together with the nitrogen atom to which they areattached, form sulfinamide, sulfonamide, amide and urea functionalityrespectively.

In one embodiment, the linking group is independently selected from—S(O)₂-L^(AA)-*, —C(O)-L^(AA)-* and —C(O)N(R¹¹)-L^(AA)-*.

In one embodiment, linking is independently selected from—S(O)₂-L^(AA)-* and —C(O)N(R¹¹)-L^(AA)-*.

It is noted that the group -L^(N)- is present only as a substituent to afurther ring nitrogen atom that is not connected to the carbon that is ato the group —X—. Where a further ring nitrogen atom is connected to thecarbon that is a to the group —X—, it is optionally substituted with—R^(L)—R^(NN). The group —R^(L)—R^(NN) does not allow for sulfinamide,sulfonamide, amide and urea groups connected to the carbon that is a tothe group —X—. The presence of sulfinamide, sulfonamide, amide and ureafunctionality is believed to be tolerated at other ring positions.

—R^(L)—

In one embodiment, each —R^(L)— is independently selected from C₁₋₁₂alkylene, C₂₋₁₂ heteroalkylene, C₃₋₁₀ cycloalkylene and C₅₋₁₀heterocyclylene.

However, where -L^(AA)- is connected to a group C₁₋₁₂ alkyl, —R^(L)— isnot C₁₋₁₂ alkylene. In a further embodiment, where -L^(AA)- is connectedto a group C₁₋₁₂ alkyl, —R^(L)— is not C₁₋₁₂ alkylene and it is notC₂₋₁₂ heteroalkylene.

Where —R^(L)— is a heteroalkylene it may be connected to —R^(AA),—R^(BB), —R^(CC), or —R^(NN) via a heteroatom of the heteroalkylenegroup, such as N, O or S, where present, or a carbon atom of theheteroalkylene group. The other point of connection is made via a carbonatom of the heteroalkylene group, for example where the heteroalkyleneis attached to a carbon atom or a heteroatom, such as N, O or S. Theother point of connection may be made via a heteroatom of theheteroalkylene group, for example where the heteroalkylene is attachedto a carbon atom. However, it is preferred that the other point ofconnection is made via a carbon atom of the heteroalkylene group,particularly where —R^(L)— is present in a group -L^(AA)-.

Where —R^(L)— is a heterocyclylene it may be connected to —R^(AA),—R^(BB), —R^(CC), or —R^(NN) via a ring nitrogen heteroatom of theheterocyclylene group, where present, or a carbon ring atom of theheterocyclylene group. The other point of connection is made via a ringcarbon atom of the heterocyclylene group, for example where theheterocyclylene is attached to a carbon atom or a heteroatom, such as N,O or S. The other point of connection may be made via a ring nitrogenheteroatom of the heterocyclylene group, for example where theheterocyclylene is attached to a carbon atom.

In one embodiment, a group —R^(L)— is independently selected from C₁₋₁₂alkylene, and C₂₋₁₂ heteroalkylene.

In one embodiment, a group —R^(L)— is independently selected from C₁₋₁₂alkylene and C₃₋₁₀ cycloalkylene.

In one embodiment, a group —R^(L)— is independently C₁₋₁₂ alkylene.

The group —R^(L)— may be substituted with one or more groups —R^(S).Thus, each C₁₋₁₂ alkylene, C₂₋₁₂ heteroalkylene, C₃₋₁₀ cycloalkylene andC₅₋₁₀ heterocyclylene is optionally substituted with one or more groups—R^(S). The specified groups may be unsubstituted or mono-substituted.The group —R^(S) may be present as a substituent to a carbon atom. Acarbon atom may be optionally mono- or di-substituted with —R^(S).

Where a nitrogen atom is present in a group, such as in aheterocyclylene group or a heteroalkylene group, that nitrogen atom maybe optionally substituted with a group —R¹².

In one embodiment, a group —R^(L)— is unsubstituted.

In one embodiment, a C₁₋₁₂ alkylene group is selected from C₁₋₆alkylene, C₁₋₄ alkylene, C₂₋₆ alkylene, and C₂₋₄ alkylene.

In one embodiment, an alkylene group is linear.

In one embodiment, a C₁₋₁₂ alkylene group is selected from —CH₂—,—CH₂CH₂—, and —CH(CH₃)—.

In one embodiment, a C₁₋₁₂ alkylene group is —CH₂—, for example when itis connected to a cycloalkyl, heterocyclyl, or aryl group.

In one embodiment, a C₂₋₁₂ heteroalkylene group is selected from C₂₋₆heteroalkylene, and C₂₋₄ heteroalklyene.

In one embodiment, a C₂₋₁₂ heteroalkylene group is selected from—CH₂O—*, —CH₂CH₂O—*, —CH₂NH—*, —CH₂CH₂NH—*, —CH₂N(R¹²)—*, and—CH₂CH₂N(R¹²)—*, where the asterisk indicates the point of attachment to—R^(AA), —R^(BB), —R^(CC), or —R^(NN). Thus, a heteroatom in theheteroalkylene group may be connected to —R^(AA), —R^(BB), —R^(CC), or—R^(NN). The other point of connection may be made via a carbon atom ofthe heteroalkylene group.

Where an S atom is present in the heteroalkylene group, it may be in theform S, S(O) or S(O)₂.

In one embodiment, the C₃₋₁₀ cycloalkylene is selected fromcyclopropylene, cyclopentylene and cyclohexylene. In one embodiment, theC₃₋₁₀ cycloalkylene is cyclohexylene.

In one embodiment, the C₅₋₁₀ heterocyclylene is C₅₋₆ heterocyclylene.

In one embodiment, the C₅₋₁₀ heterocyclylene is selected frompiperidinene, piperazinene, morpholinene and thiomorpholinene. Theheterocyclylene may be connected to —R^(AA), —R^(BB,) —R^(CC), or—R^(NN) via a ring carbon or ring nitrogen atom. The other point ofconnection may be made via a carbon atom of the heterocyclylene group.

A nitrogen atom, where present, is optionally substituted with —R¹².

Where an S atom is present in the heterocyclylene group, it may be inthe form S, S(O) or S(O)₂.

—R^(AA), —R^(BB), —R^(CC), and —R^(NN)

Each of —R^(AA), —R^(BB), —R^(CC,) and —R^(NN), where present, isindependently selected from C₁₋₁₂ alkyl, C₃₋₁₀ cycloalkyl, C₄₋₁₀heterocyclyl, and C₅₋₁₂ aryl.

In one embodiment, a C₁₋₁₂ alkyl group is selected from C₁₋₆ alkyl, C₁₋₇alkyl, C₁₋₄ alkyl, C₂₋₆ alkyl, C₂₋₄ alkyl, C₃₋₁₀ alkyl, C₃₋₇ alkyl,C₄₋₁₀ alkyl and C₆₋₁₀ alkyl.

In one embodiment, an alkyl group is linear.

In one embodiment, an alkyl group is branched.

In one embodiment, the C₁₋₁₂ alkyl group does not include C₈ alkyl.

In one embodiment, a C₃₋₁₀ cycloalkyl group is C₃₋₆ cycloalkyl or C₅₋₆cycloalkyl.

In one embodiment, a C₃₋₁₀ cycloalkyl group is cyclohexyl.

In one embodiment, a C₄₋₁₀ heterocyclyl group is selected from C₅₋₁₀heterocyclyl, C₆₋₁₀ heterocyclyl, C₅₋₇ heterocyclyl and C₅₋₆heterocyclyl.

In one embodiment, a C₄₋₁₀ heterocyclyl group is selected fromtetrahydrofuranyl, pyrrolidinyl, tetrahydropyranyl, morpholinyl,thiomorpholinyl, piperidinyl and piperazinyl.

In one embodiment, a C₄₋₁₀ heterocyclyl group is selected fromtetrahydropyanyl, morpholinyl, piperidinyl and piperazinyl.

Where an S atom is present in a heterocyclyl group, it may be in theform S, S(O) or S(O)_(2.)

A nitrogen atom, where present, is optionally substituted with —R¹².

A heterocyclyl group may be connected via a ring nitrogen heteroatomatom or a ring carbon atom. Where the heterocyclyl group is asubstituent to a nitrogen atom (e.g. present in the group —R^(L)—), theheterocyclyl group is connected to that nitrogen atom via a ring carbonatom.

An aryl group, particularly a heteroaryl group such as indole, may beconnected via a ring nitrogen heteroatom atom or a ring carbon atom.Where the heteroaryl group is a substituent to a nitrogen atom, theheteroaryl group is connected to that nitrogen atom via a ring carbonatom. Typically, the aryl group is connected via a ring carbon atom.

In one embodiment, the C₅₋₁₂ aryl is selected from C₆₋₁₂ carboaryl andC₅₋₁₂ heteroaryl.

In one embodiment, the C₅₋₁₂ aryl is selected from phenyl, pyridyl, andnaphthyl, optionally together with 1,3-benzodioxolyl and pyridonyl.

In one embodiment, the C₆₋₁₂ carboaryl is selected from phenyl,naphthyl, chromanyl, iso-chromanyl and 1,3-benzodioxolyl. The chromanyl,iso-chromanyl and 1,3-benzodioxolyl groups are connected via an aromaticring carbon atom. Further discussion about the meaning of the termcarboaryl is provided below with reference to the group -G.

In one embodiment, the C₅₋₁₂ carboaryl is selected from phenyl andnaphthyl,

In one embodiment, the C₅₋₁₂ heteroaryl is selected from C₅₋₁₀heteroaryl and C₅₋₆ heteroaryl.

In one embodiment, the C₅₋₁₂ heteroaryl is selected from the groupconsisting of independently furanyl, thienyl, pyrrolyl, imidazolyl,pyrazolyl, oxazolyl, isoxazolyl, thiazolyl, isothiazolyl, pyridyl,pyrimidinyl, pyrazinyl, pyridazinyl, quinolinyl, isoquinolinyl, indolyland pyridonyl.

Further discussion about the meaning of the term heteroaryl is providedbelow with reference to the group -G.

Each C₁₋₁₂ alkyl, C₃₋₁₀ cycloalkyl, C₄₋₁₀ heterocyclyl, and C₅₋₁₂ arylgroup is optionally substituted with —R^(S) at carbon and —R¹² atnitrogen, where present. Each group may have one, two, three or moregroups —R^(S). In one embodiment, a heterocyclyl group or a heteroarylgroup may have one, two, three or more groups —R¹².

In one embodiment, a group is mono-subsituted.

In one embodiment, a group is unsubstituted.

The group —R^(S) is present as a substituent to a carbon atom. A carbonatom may be optionally mono- or di-substituted with —R^(S).

Where a nitrogen atom is provided, such as in a heterocyclyl group or aheteroaryl group, that nitrogen may be optionally substituted with agroup —R¹².

In one embodiment, —R^(AA) is independently selected from C₁₋₁₂ alkyland C₅₋₁₂ aryl.

In one embodiment, —R^(AA) is independently C₁₋₁₂ alkyl. In oneembodiment, —R^(AA) is independently C₂₋₁₂ alkyl, such as C₃₋₁₂ alkyl.

In one embodiment, —R^(AA) is independently C₅₋₁₂ aryl.

In one embodiment, —R^(BB) is independently selected from C₁₋₁₂ alkyl,C₄₋₁₀ heterocyclyl, and C₅₋₁₂ aryl, for example when -L^(B)- is acovalent bond, or for example when —R^(A) is hydrogen.

In one embodiment, —R^(BB) is independently selected from C₁₋₁₂ alkyl,C₃₋₁₀ cycloalkyl, C₄₋₁₀ heterocyclyl, and C₅₋₁₂ aryl, for example when—R^(B) is a substituent to a heterocycle ring carbon atom.

In one embodiment, —R^(BB) is independently selected from C₁₋₁₂ alkyland C₅₋₁₂ aryl.

In one embodiment, —R^(BB) is independently C₁₋₁₂ alkyl. In oneembodiment, —R^(BB) is independently C₂₋₁₂ alkyl, such as C₃₋₁₂ alkyl.

In one embodiment, —R^(BB) is independently C₅₋₁₂ aryl.

In one embodiment, a group —R^(NN) is independently selected from C₁₋₁₂alkyl and C₅₋₁₂ aryl.

In one embodiment, —R^(NN) is independently C₁₋₁₂ alkyl. In oneembodiment, —R^(NN) is independently C₂₋₁₂ alkyl, such as C₃₋₁₂ alkyl.

In one embodiment, —R^(NN) is independently C₅₋₁₂ aryl.

—R^(S)

The group —R^(S) is an optional substituent to each C₁₋₁₂ alkyl, C₃₋₁₀cycloalkyl, C₄₋₁₀ heterocyclyl, C₅₋₁₂ aryl, C₁₋₁₂ alkylene, C₂₋₁₂heteroalkylene, C₃₋₁₀ cycloalkylene and C₅₋₁₀ heterocyclylene group.Where a group is optionally substituted, it may be optionallysubstituted with one or more groups —R^(S). A group may be optionallymono-substituted with —R^(S).

The group —R^(S) is an optional substituent to a carbon atom. A carbonatom may be mono-, di- or tri-substituted.

In one embodiment, each —R^(S), where present, is independently selectedfrom —OH, —OR¹², halo, —R¹², —NHR¹², —NR¹²R¹³, —C(O)R¹², —COOH and—COOR¹².

In one embodiment, each —R^(S), where present, is independently selectedfrom —OR¹², halo, —R¹², —NHR¹², —NR¹²R^(13,) —C(O)R¹², —COOH and—COOR¹².

In one embodiment, each —R^(S), where present, is independently selectedfrom —OR¹², halo, and —R¹².

Where —R^(S) is a substituent to an alkyl group, —R^(S) is not —R¹².

Where —R^(S) is halo it may be selected from fluoro, chloro, bromo andiodo, such as chloro and bromo, such as chloro.

In one embodiment, where a carbon atom is di-substituted with —R^(S),these groups may together with the carbon to which they are attachedform a C₃₋₆ carbocycle or a C₅₋₆ heterocycle, where the carbocycle andthe heterocycle are optionally substituted with one or more groups —R¹².Where an S atom is present in the heterocycle group, it may be in theform S, S(O) or S(O)₂.

In one embodiment, a C₃₋₆ carbocycle is cyclopentane or cyclohexane,such as cyclohexane.

In one embodiment, a C₅₋₆ heterocycle is selected from piperidine,piperazine, morpholine, thiomorpholine, tetrahydrofuran andtetrahydropyran.

—R¹² and —R¹³

Each —R¹² and —R¹³ is independently C₁₋₆ alkyl, C₁₋₆ haloalkyl, phenylor benzyl.

Where —R¹² and —R¹³ are both attached to N, they may together with the Natom form a 5- or 6-membered heterocycle, such as pyrrolidine,piperazine, piperidine, thiomorpholine or morpholine. The heterocyclicring is optionally substituted with C₁₋₆ alkyl, C₁₋₆ haloalkyl, phenylor benzyl.

In one embodiment, a —R¹² or —R¹³ group is independently C₁₋₆ alkyl,phenyl or benzyl.

In one embodiment, a —R¹² or —R¹³ group is independently C₁₋₆ alkyl.

In one embodiment, the C₁₋₆ alkyl is selected from methyl and ethyl.

In one embodiment, the C₁₋₆ haloalkyl is —CF₃.

—R¹¹

In one embodiment, a group —R¹¹ is independently selected from hydrogen,methyl and ethyl.

In one embodiment, —R¹¹ is independently hydrogen.

Embodiments Relating to Compounds (I) and (II) from WO 2014/188178

The compounds of the present case may use a group —R⁵ from compounds (I)and (II) of WO 2014/188178 as a group —R^(T).

—X— and —R⁵

The compounds of formula (I) do not encompass the deacylated versions ofPolymyxin B (Deacylpolymyxin B-DAPB), D, E (Deacylcolistin-DAC) or M, orCirculin A. The compounds of formula (I) do not encompass thenonapeptide versions of Polymyxin B (PMBN), D, E or M, or Circulin A.

In one embodiment, —X— and —R⁵ together are not an α-amino acid residue,for example when -A- is a covalent bond. An α-amino acid residue is agroup where —X— is —C(O)— and —R⁵ has a group —NR⁶R⁷ (such as —NH₂) as asubstituent to the carbon atom that is α to the group —X—.

In one embodiment, —X— and —R⁵ together are not Thr, Ser,α,γ-diaminobutyric acid (Dab) or α,β-diaminopropionic acid (Dap)residues.

In one embodiment, for example where the core of the compound of formula(I) is Polymyxin B, X and R⁵ together are not Lys, Arg, Dap, Ser, Phe,Trp, Leu or Ala residues.

In one embodiment, —X— and —R⁵ together are not Lys, Arg, Dap, Ser, Phe,Trp, Leu, Ala α,γ-diaminobutyric acid (Dab) or α,β-diaminopropionic acid(Dap) residues.

In one embodiment, —X— and —R⁵ together are not Ala, Ser, Thr, Val, Leu,Ile, Pro, Phe, Tyr, Trp, His, Lys or Arg residues.

In one embodiment, —X— and —R⁵ together are not Ala, Ser, Thr, Val, Leu,Ile, Pro, Phe, Tyr, Trp, His, Lys, Arg,α,γ-diaminobutyric acid (Dab) ora,8-diaminopropionic acid (Dap) residues.

In one embodiment, —X— and —R⁵ together are not an α-amino acid, forexample a D or L α-amino acid, for example a L α-amino acid.

In one embodiment, —R⁵ is not diaminophenyl, for example,3,5-diaminophenyl when —X— is —C(O)—.

—R⁵

In one embodiment, —R⁵ is G-L²-L¹-.

—R⁵ may be G-L¹-, for example where -L²- is a covalent bond.

—R⁵ may be G-L²-, for example where -L¹- is a covalent bond.

—R⁵ may be -G, for example where -L¹- and -L²- are covalent bonds.

In one embodiment, —R⁵ is D-L¹-.

—R⁵ may be -D, for example where -L¹- is a covalent bond.

In one embodiment, —R⁵ has one, two or three hydroxyl and/or —NR⁶R⁷groups. These groups may be provided on any group within —R⁵, including-G, -D, -L¹- and -L²-. In one embodiment, these groups are provided assubstituents to -G, -D, and -L¹-.

It is noted that the hydroxyl and —NR⁶R⁷ groups are optionallysubstituents to the group D-L¹-.

Where the hydroxyl and —NR⁶R⁷ substituents are discussed below, they maybe referred to as substituents to —R⁵.

In one embodiment, the one, two or three hydroxyl and/or —NR⁶R⁷ groupsare optional substituents to —R⁵. This may be the case where -L¹- is anitrogen-containing C₂₋₁₂ heteroalkylene, and/or -L²- is anitrogen-containing C₄₋₁₀ heterocyclylene, and/or -D is anitrogen-containing C₄₋₁₀ heterocyclyl.

In one embodiment, —R⁵ has at least 5, at least 6, at least 7 or atleast 8 carbon atoms present.

In one embodiment, —R⁵ has 1, 2, or 3 nitrogen atoms present. In oneembodiment, the nitrogen atom is a basic nitrogen atom. The nitrogenatom may be present as NH. In one embodiment, —R⁵ has 1, 2, or 3 oxygenatoms present.

In one embodiment, —R⁵ is not aminocyclohexyl, for example when -A- is acovalent bond, —X— is —C(O)— and —R¹, —R² and —R³ are amino acidresidues of polymyxin B.

Okimura et al. describe Polymyxin B nonapeptide compounds havingaminocyclohexyl groups at the N terminal. These compounds are notdescribed for use in combination with an active agent,

In one embodiment, —R⁵ is not an aminocyclohexyl group selected from thegroups consisting of cis-2-aminocylcohexyl, trans-2-aminocylcohexyl,cis-3-aminocyclohexyl, cis-4-aminocylcohexyl, andtrans-4-aminocylcohexyl. Additionally or alternatively, —R⁵ is nottrans-3-aminocylcohexyl.

Linker: -L²-L¹- and -L¹-

Within the groups G-L²-L¹- and D-L¹-, -L²-L¹- and -L¹- may be regardedas linkers connecting the group —X— to -G or -D. The linker may beabsent, for example where -L¹- and -L²- are covalent bonds.

-L²-L¹- in G-L²-L¹-

In one embodiment, -L¹- and -L²- are both covalent bonds. Thus, thegroup -G is connected directly to —X—. Here, the hydroxyl or aminogroups (such as one, two or three hydroxyl and/or —NR⁶R⁷ groups) must bepresent on -G.

Where -L¹- is a nitrogen-containing C₂₋₁₂ heteroalkylene and/or -L²- isa nitrogen-containing C₄₋₁₀ heterocyclylene, it is not necessary forG-L²-L¹- to be substituted with one, two or three hydroxyl and/or —NR⁶R⁷groups.

-L¹- in D-L¹-

In one embodiment, -L¹- is a covalent bond. Thus, the group -D isconnected directly to —X—.

Where the group D-L¹- is substituted with a hydroxyl group or an aminogroup (such as one, two or three hydroxyl and/or —NR⁶R⁷ groups), thegroups must be present on -D.

Where -L¹- is a nitrogen-containing C₂₋₁₂ heteroalkylene and/or -D is anitrogen-containing C₄₋₁₀ heterocyclyl it is not necessary for D-L¹- tobe substituted with one, two or three hydroxyl and/or —NR⁶R⁷ groups.

-L¹-

In one embodiment, -L¹- is a covalent bond or a C₁₋₁₂ alkylene group.

In one embodiment, -L¹- is a covalent bond.

In one embodiment, -L¹- is a C₁₋₁₂ alkylene group or a C₂₋₁₂heteroalkylene group.

In one embodiment, -L¹- is a C₁₋₁₂ alkylene group.

In one embodiment, -L¹- is C₁₋₁₂ alkylene, for example C₁₋₆, C₁₋₄ orC₁₋₂ alkylene.

In one embodiment, -L¹- is —CH₂- or —CH₂CH₂—.

In one embodiment, -L¹- is C₂₋₁₂ alkylene, for example C₂₋₆ or C₂₋₄alkylene.

In one embodiment, -L¹- is C₃₋₁₂ alkylene, for example C₃₋₆, C₄₋₁₂,C₅₋₁₂ or C₆₋₁₂ alkylene.

The alkylene group is a saturated, aliphatic alkylene group.

The alkylene group may be a linear or a branched alkylene group. In oneembodiment, the alkylene group is linear.

Where -L¹- is an alkylene group and R⁵ is substituted with one, two orthree hydroxyl and/or —NR⁶R⁷ groups, one or more of the substituents maybe substituents to the alkylene group.

In one embodiment, the alkylene group has one, two or threesubstituents.

In one embodiment, the alkylene group has one or two substituents, suchas one substituent.

In one embodiment, the number of substituents on the alkylene group isno greater than the number of carbon atoms in the alkylene group. Thus,where -L¹- is a C₂ alkylene group it may be substituted with no morethan two substituents.

Additional substituents, where present, may be located on -G or -D,where appropriate.

In one embodiment, the alkylene group is unsubstituted.

In one embodiment, -L¹- is C₂₋₁₂ heteroalkylene. A heteroalkylene groupis an alkylene group where one or more, such as two or three, or more,of the carbon atoms is replaced with a heteroatom selected from N, O andS. The superscript e.g. 4 in C₄ refers to the total number of carbonatoms and heteroatoms. The heteroatom of the heteroalkylene group isunderstood not to be a pendant amino, hydroxyl or thiol group.

In one embodiment, the heteroalkylene group contains one or twoheteroatoms, for example one or two nitrogen atoms, such as one or two—NH—.

In one embodiment, heteroalkylene group is a nitrogen-containingheteroalkylene group.

The heteroatom may be provided as an interruption of the alkylene chaine.g. —CH₂—NH—CH₂—.

The heteroatom may be provided as a terminal group for connection to—X—, -L²-, -G or -D, for example —CH₂—CH₂—NH— or —NH—CH₂—CH₂—. In theseembodiments, the heteroatom is bonded to a carbon atom in —X—, -L²-, -Gor -D.

In one embodiment, the heteroatom of the heteroalkylene group is notcovalently bonded to the group —X—.

In one embodiment, the heteroatom of the heteroalkylene group is notcovalently bonded to the group -L²-, -G or -D, where present. In analternative embodiment, a heteroatom of the heteroalkylene group, suchas —NH—, is covalently bonded to the group -L²-, -G or -D, wherepresent.

In one embodiment, -L¹- is C₂₋₁₂ heteroalkylene, for example C_(2-6,)C_(2-4,) C_(3-6,) C_(3-12,) C₄₋₆ or C₄₋₁₂ heteroalkylene.

The heteroalkylene group is a saturated, aliphatic heteroalkylene group.

The heteroalkylene group may be a linear or a branched heteroalkylenegroup. In one embodiment, the heteroalkylene group is linear.

In one embodiment, -L¹- is —NH—CH₂CH₂—NH—CH₂—.

In one embodiment, -L¹- is —CH₂—NH—CH₂CH₂—.

In one embodiment, the heteroalkylene group is unsubstituted.

In one embodiment, the heteroalkylene group is substituted, for examplewith one or two hydroxyl and/or —NR⁶R⁷ groups, such as one hydroxyl or—NR⁶R⁷ group. The substituents are provided on the carbon atoms withinthe heteroalkylene group

In one embodiment, the number of substituents on the heteroalkylenegroup is no greater than the number of carbon atoms in theheteroalkylene group.

Where the heteroalkylene group is substituted, the substituents arepreferably not provided on a carbon atom that is covalently bonded to aheteroatom of the heteroalkylene group.

Where the heteroalkylene group is substituted, the substituents may beprovided on a carbon atom that is not bonded to a heteroatom.

-L²-

In one embodiment, -L²- is a covalent bond.

In one embodiment, -L²- is a C₄₋₁₀ heterocyclylene group, for examplewhen -L¹- is a C₁₋₁₂ alkylene group.

In one embodiment, -L²- is a C₄₋₇ heterocyclylene group, for example aC₅₋₇ or C₅₋₆ heterocyclylene group.

In one embodiment, the C₄₋₁₀ heterocyclylene contains one or twoheteroatoms selected from N, S and O. Where a S atom is present, it maybe in the form S, S(O) or S(O)₂. Where an N atom is present it may be inthe form NH or NR, where —R is C₁₋₄ alkyl, such as methyl or ethyl.

In one embodiment, the heterocyclylene group is a nitrogen-containingheterocyclylene.

The heterocyclylene group may contain one or two nitrogen atoms. Eachnitrogen atom may be optionally substituted with C₁₋₄ alkyl, whereappropriate. In one embodiment the heterocyclylene group contains onlynitrogen heteroatoms.

In one embodiment, the heterocyclylene group is unsubstituted. Thus, thehydroxyl and/or —NR⁶R⁷ groups are provided elsewhere, as required, forexample on -L¹-, where present, or on -G or -D.

In one embodiment, the heterocyclylene is connected to -L¹- or —X— via acarbon atom or nitrogen atom, where present, of the heterocyclylenering.

In one embodiment, the heterocyclylene is connected to -G via a carbonatom or nitrogen atom, where present, of heterocyclylene ring.

In one embodiment, -L²- is selected from piperidinylene, piperazinyleneand pyrroldinylene.

In one embodiment, -L²- is selected from piperidinyl-1,4-ene,piperazinyl-1,4-ene and pyrroldinyl-1,3-ene.

Location of Hydroxyl and —NR⁶R⁷ Substituents

In one embodiment, a group —R⁵, such as G-L²-L¹- or D-L¹-, may besubstituted with one, two or three hydroxyl groups.

In one embodiment, —R⁵ is substituted with one hydroxyl group.

In one embodiment, a group —R⁵ may be substituted with one, two or threegroups —NR⁶R⁷.

In one embodiment, —R⁵ is substituted with one —NR⁶R⁷ group.

In one embodiment, —R⁵ is substituted with two or three groups —NR⁶R⁷.

In one embodiment, a group —R⁵ may be substituted with one or two groups—NR⁶R⁷, and one, two or three hydroxyl groups.

In one embodiment, —R⁵ is substituted with one —NR⁶R⁷ group and onehydroxyl group.

In one embodiment, a hydroxyl group, such as one, two or three hydroxylgroups, are substituents to -G.

In one embodiment, a hydroxyl group, such as one, two or three hydroxylgroups, are substituents to -D.

In one embodiment, a hydroxyl group, such as one, two or three hydroxylgroups, are substituents to -L¹-, where appropriate, for example where-L¹- is alkylene or heteroalkylene.

In one embodiment, a hydroxyl group, such as one, two or three hydroxylgroups, are substituents to -L²-, where appropriate, for example where-L²- is heterocyclylene.

In one embodiment, a —NR⁶R⁷ group, such as one, two or three —NR⁶R⁷groups, are substituents to -G.

In one embodiment, a —NR⁶R⁷ group, such as one, two or three —NR⁶R⁷groups, are substituents to -D.

In one embodiment, a —NR⁶R⁷ group, such as one, two or three —NR⁶R⁷groups, are substituents to -L¹-, where appropriate, for example where-L¹- is alkylene or heteroalkylene.

In one embodiment, a —NR⁶R⁷ group, such as one, two or three —NR⁶R⁷groups, are substituents to -L²-, where appropriate, for example where-L²- is heterocyclylene.

In one embodiment, G-L²-L¹- is optionally substituted with (i), (ii) and(iii), for instance where L¹- is a nitrogen-containing C₂₋₁₂heteroalkylene and/or -L²- is a nitrogen-containing C₄₋₁₀heterocyclylene. In one embodiment, the proviso does not apply,therefore that (i), (ii) and (iii) are not optional substituents.

In one embodiment, G-L²-L¹- is substituted with:

-   -   (i) one or two hydroxyl groups, or    -   (ii) one or two groups —NR⁶R⁷, or    -   (iii) one group —NR⁶R⁷ and one hydroxyl groups,    -   with the proviso that (i), (ii) and (iii) are optional        substituents when -L¹- is a nitrogen-containing C₂₋₁₂        heteroalkylene and/or -L²- is a nitrogen-containing C₄₋₁₀        heterocyclylene.

For the avoidance of doubt, where a group —R⁵ is said to be substitutedwith one hydroxyl group (—OH), no further hydroxyl groups are presentwithin —R⁵. Likewise, where a group —R⁵ is said to be substituted withone group —NR⁶R⁷, no further groups —NR⁶R⁷ are present within —R⁵.Similarly, where —R⁵ has two or three hydroxyl or —NR⁶R⁷ groups, thetotal number of hydroxyl or —NR⁶R⁷ groups is two or three.

As described herein, where a group —NR⁶R⁷ is present, it is preferredthat it is not a substituent at a carbon atom a to the group —X—.

As described in further detail below, where a hydroxyl group is present,it is preferred that it is a substituent at a carbon atom a to the group—X—.

In one embodiment, where —R⁵ has more than one substituent, thesubstituents are not located on the same carbon atom.

A carboxylic group (—COOH) is not to be construed as a hydroxyl group inthe present case.

Where -L¹- has more than two carbon atoms present (e.g. C₂₋₁₂ alkyleneor C₃₋₁₂ heteroalkylene) a substituent, where present, may be providedat a carbon atom that is α to the group —X—.

Similarly, where -L¹- and -L²⁻ are both covalent bonds, and -G is C₂₋₁₂alkyl, the group C₂₋₁₂ alkyl may have a substituent at a carbon atomthat is a to the group —X—.

In one embodiment, -L¹- is substituted with a hydroxyl group (forexample one, two or three hydroxyl groups) and the hydroxyl group isprovided at the carbon atom that is a to the group —X—. Examples ofcompounds having such a substitution include Example compound 27 in thepresent case. The present inventors have found that compounds having ahydroxyl group at the α carbon have a particularly improved potentiatingactivity compared to those compounds where the hydroxyl group isconnected, for example, to a carbon atom that is not α the group —X—,for example β or γ to the group —X—, such as Example compound 25.

Similarly, where -L¹- and -L²- are both covalent bonds, and -G is C₂₋₁₂alkyl, the group C₂₋₁₂ alkyl may have a hydroxyl group provided at acarbon atom that is a to the group —X—.

Where -L¹- has more than two carbon atoms present (e.g. C₂₋₁₂ alkyleneor C₃₋₁₂ heteroalkylene) a substituent, where present, may be providedat a carbon atom that is not α to the group X. For example, thesubstituent may be provided at a carbon atom that is β or γ to the group—X—. In one embodiment, no substituent is provided at the carbon atom αto the group —X—.

Similarly, where -L¹- and -L²- are both covalent bonds, and -G is C₂₋₁₂alkyl, the group C₂₋₁₂ alkyl may have a substituent that is not providedat a carbon atom that is a to the group —X—. For example, thesubstituent may be provided at a carbon atom that is β or γ to the group—X—.

In one embodiment, -L¹- is substituted with an amino group (for exampleone or two amino groups) and the amino group (i.e. —NR⁶R⁷) is providedat a carbon atom that is not α to the group X. Examples of compoundshaving such a substitution include Example compound 10 in the presentcase. The present inventors have found that compounds having an aminogroup at the α carbon, such as Example compound 40, have particularlyreduced potentiating activity compared to those compounds where theamino group is connected, for example, to a carbon atom that is γ or γto the group —X—.

Similarly, where -L¹- and -L²- are both covalent bonds, and -G is C₂₋₁₂alkyl, the group C₂₋₁₂ alkyl may have an amino group provided at acarbon atom that is not α to the group —X—, for example β or γ to thegroup —X—.

In one embodiment, an amino or hydroxyl substituent is provided at aterminal carbon of the group -L¹- (e.g. C₂₋₁₂ alkylene or C₂₋₁₂heteroalkylene) or the terminal carbon of the —C₂₋₁₂ alkyl, wherepresent.

In one embodiment, the group -L¹- in D-L¹- is a covalent bond. Thus -D,which is a C₄₋₁₀ heterocyclyl, is connected directly to the group —X—.

In one embodiment, the group -L²- is a C₄₋₁₀ heterocyclyl. Where -L¹- isa covalent bond, -L²- is connected directly to the group —X—.

The connection of either these heterocyclyl groups to —X— is discussedbelow.

In one embodiment, an atom that is a to the group —X— may be a ringcarbon atom of the heterocyclyl group. A ring heteroatom of theheterocyclyl group may be covalently bonded to the ring carbon atom thatis a to the group —X— i.e. the ring heteroatom is β to the group —X—. Inone embodiment, a ring heteroatom β to the group X is O or S, such as O.In one embodiment the ring heteroatom β to the group —X— is not N.

In one embodiment, a ring heteroatom γ to the group X is O, S or N.

In one embodiment, where -L¹- and -L²- are both covalent bonds, and -Gis a C₅₋₁₂ heteroaryl, the heteroaryl may be connected to the group —X—via a ring carbon atom, which is α to the group —X—). In one embodiment,a ring heteroatom, such as N, is not connected to the carbon atom whichis a to the group —X—. Alternatively, a ring heteroatom, such as O or S,is connected to the carbon atom which is α to the group —X—.

In one embodiment, the group G-L²-L¹- has one, two or three hydroxylgroup and/or —NR⁶R⁷ substituents. These substituents may be provided onone or more of the groups -G-, -L²- or -L¹-, where appropriate. In oneembodiment, the substituents are provided on -G- and/or -L¹-. Where -L¹-is C₂₋₁₂ heteroalkylene, the one, two or three hydroxyl group and/or—NR⁶R⁷ substituents are optional.

The group D-L¹- optionally has one, two or three hydroxyl group and/or—NR⁶R⁷ substituents.

Where the substituents are present they may be provided on -D or -L¹-,where appropriate.

In one embodiment, —R⁵ is G-L²-L¹-, where -G is C₅₋₁₂ aryl.

In one embodiment, —R⁵ is G-L²-L¹-, where -G is C₃₋₁₀ cycloalkyl or—C₂₋₁₂ alkyl, or —R⁵ is D-L¹-, where D is C₄₋₁₀ heterocyclyl.

In one embodiment, G-L²-L¹- is substituted with (i) one, two or threehydroxyl groups, (ii) one, two or three groups —NR⁶R⁷, or (iii) one ortwo groups —NR⁶R⁷, and one, two or three hydroxyl groups. Where an arylgroup is present in G-L²-L¹- it is independently optionally substitutedone or more substituents selected from —C₁₋₄ alkyl, halo, —CN, —NO₂,—CF₃, —NR¹⁰C(O)R¹⁰, —CON(R¹⁰)_(2,) —COOR⁹, —OCOR¹⁰, —NR¹⁰COOR¹⁰,—OCON(R¹⁰)₂, —OCF₃, —NR¹⁰CON(R¹⁰)_(2,) —OR⁹, —SR⁹, —NR¹⁰SO₂R¹⁰,—SO₂N(R¹⁰)₂ and —SO₂R¹⁰ where each —R⁹ is independently —C₁₋₄ alkyl andeach —R¹⁰ is independently —H or —C₁₋₄ alkyl.

In one embodiment, D-L¹- is optionally substituted with (i) one, two orthree hydroxyl groups, (ii) one, two or three groups —NR⁶R⁷, or (iii)one, two or three groups —NR⁶R⁷, and one, two or three hydroxyl groups.

In one embodiment, D-L¹- is substituted with (i) one, two or threehydroxyl groups, (ii) one, two or three groups —NR⁶R⁷, or (iii) one, twoor three groups —NR⁶R⁷, and one, two or three hydroxyl groups.

The groups C₃₋₁₀ cycloalkyl C₂₋₁₂ alkyl and C₄₋₁₀ heterocyclyl may besubstituted with hydroxyl and/or —NR⁶R⁷ groups. Where the cycloalkyl orheterocyclyl groups include a fused aromatic ring, that aromatic ringmay be optionally substituted with the optional substituents describedherein. The optional further substituents do not include hydroxyl and/or—NR⁶R⁷ groups.

The group C₅₋₁₂ aryl is substituted with hydroxyl and/or —NR⁶R⁷ groupsand the C₅₋₁₂ aryl group is optionally further substituted. The optionalfurther substituents do not include hydroxyl and/or —NR⁶R⁷ groups.

It is not essential for the C₃₋₁₀ cycloalkyl, C₂₋₁₂ alkyl, C₅₋₁₂ aryland C₄₋₁₀ heterocyclyl groups of -G and -D to be substituted withhydroxyl and/or —NR⁶R⁷ groups. In one embodiment, the hydroxyl and/or—NR⁶R⁷ groups may be provided on the linker elements of —R⁵ e.g. -L¹-and/or -L²-, where present.

Where —R⁵ contains a heterocyclyl or heteroalkylene group, for exampleas part of -L¹-, -L²- or -D, such as nitrogen-containing heterocyclyl orheteroalkylene groups, the hydroxyl and/or —NR⁶R⁷ groups may beoptional.

In one embodiment, G-L²-L¹- is substituted with:

-   -   (i) one, two or three hydroxyl groups, or    -   (ii) one, two or three groups —NR⁶R⁷, or    -   (iii) one or two groups —NR⁶R⁷, and one, two or three hydroxyl        groups,    -   with the proviso that (i), (ii) and (iii) are optional        substituents when -L¹- is a nitrogen-containing C₂₋₁₂        heteroalkylene and/or -L²- is a nitrogen-containing C₄₋₁₀        heterocyclyl.

In one embodiment, G-L²-L¹- is substituted with:

-   -   (i) one, two or three hydroxyl groups, or    -   (ii) one, two or three groups —NR⁶R⁷, or    -   (iii) one or two groups —NR⁶R⁷, and one, two or three hydroxyl        groups.

-D

The N terminal substituent of the polymyxin compound may include a C₄₋₁₀heterocyclyl group (“heterocyclyl group”). Thus, in one embodiment, —R⁵includes the group -D, which is a C₄₋₁₀ heterocyclyl.

In one embodiment, -D is a nitrogen-containing heterocyclyl group. Insuch embodiments the hydroxyl and —NR⁶R⁷ groups are optional.

Where a heterocyclyl group does not contain a nitrogen atom, either orboth of -D and -L¹- must be substituted with one, two or three hydroxyland/or —NR⁶R⁷ groups or -L¹- must be a nitrogen-containing C₂₋₁₂heteroalkylene.

In one embodiment, C₄₋₁₀ heterocyclyl is C₄₋₆ or C₅₋₆ heterocyclyl, suchas C₅ heterocyclyl or C₆ heterocyclyl.

In one embodiment, the C₄₋₁₀ heterocyclyl contains one or twoheteroatoms selected from N, S and O. Where a S atom is present, it maybe in the form S, S(O) or S(O)₂. Where an N atom is present it may be inthe form NH or NR, where R is C₁₋₄ alkyl, such as methyl or ethyl.

In one embodiment, the heterocyclyl group is a nitrogen-containingheterocyclyl group.

In one embodiment, the C₄₋₁₀ heterocyclyl is piperidinyl, piperazinyl,morpholinyl, dioxanyl, thiomorpholinyl (including oxidisedthiomorpholinyl), or pyrroldinyl.

In one embodiment, the C₄₋₁₀ heterocyclyl is piperidinyl, piperazinyl,thiomorpholinyl (including oxidised thiomorpholinyl), pyrroldinyl ormorpholinyl.

In one embodiment, the C₄₋₁₀ heterocyclyl is piperidinyl, piperazinyl orpyrroldinyl.

Where a heterocyclyl is present it is connected to -L¹- or —X— via aring carbon atom or a ring N atom, where present. In one embodiment, theheterocyclyl is connected via a ring carbon atom. In another embodiment,the heterocyclyl is connected via a ring nitrogen atom, where present.

Where a heterocyclyl is substituted with one, two or three hydroxyland/or —NR⁶R⁷ groups, these groups are substituents to the heterocyclylring carbon atoms.

In one embodiment, a hydroxyl or —NR⁶R⁷ group, where present, is asubstituent to a ring carbon atom that is β to a ring heteroatom.

In one embodiment, the heterocyclyl, if substituted, has a maximum ofone or two substituents, which may be the same or different.

In one embodiment, the total number of carbon atoms in the heterocyclylgroup, together with the total number of carbon atoms present in —R⁶ and—R⁷ (where present) is at least 5, at least 6, at least 7 or at least 8.

For the avoidance of doubt, the index “C_(x-y)” in terms such as “C₄₋₇heterocyclyl”, and the like, refers to the number of ring atoms, whichmay be carbon atoms or heteroatoms (e.g., N, O, S). For example,piperidinyl is an example of a C₆heterocycyl group.

The term “heterocyclyl” in reference to the group -D refers to a group(1) which has one or more heteroatoms (e.g., N, O, S) forming part of aring system, wherein the ring system comprises one ring or two or morefused rings, wherein at least one ring of the ring system is anon-aromatic ring, and (2) which is attached to the rest of the moleculeby a non-aromatic ring atom (i.e., a ring atom that is part of anon-aromatic ring that is part of the ring system). For example:piperidino and piperidin-4-yl are both examples of a C₆heterocycylgroup; 2,3-dihydro-1H-indol-1-yl is an example of a C₉heterocycyl group;and both decahydro-quinolin-5-yl and 1,2,3,4-tetrahydroquinolin-4-yl areexamples of a C₁₀heterocyclyl group.

The optional substituents are those described as optional substituentsfor the C₅₋₁₂ aryl group.

In one embodiment, where a heterocyclyl group contains two or more fusedrings, each ring is non-aromatic.

In one embodiment, the heterocyclyl group comprises one ring.

-G

The group -G is selected from C₃₋₁₀ cycloalkyl, C₂₋₁₂ alkyl and C₅₋₁₂aryl. A description of each of these is given below. The groupsdiscussed below may be used together with any -L¹- and -L²-, asappropriate.

C₃₋₁₀ cycloalkyl

The N terminal substituent of the polymyxin compound may include a C₃₋₁₀cycloalkyl group (“cycloalkyl group”). Thus, -G may be C₃₋₁₀ cycloalkyl.

When -G is C₃₋₁₀ cycloalkyl, -L¹- may be a covalent bond, C₁₋₁₂ alkyleneor C₂₋₁₀ heteroalkylene, for example a covalent bond or C₁₋₁₂ alkylene.

When -G is C₃₋₁₀ cycloalkyl, -L²- may be a covalent bond or C₄₋₁₂heterocyclyl, for example a covalent bond.

In one embodiment, C₃₋₁₀ cycloalkyl is a C₃₋₈ or C₃₋₆ cycloalkyl.

In one embodiment, C₃₋₁₀ cycloalkyl is cyclopentyl or cyclohexyl.

In one embodiment, the cycloalkyl, if substituted, has a maximum of oneor two substituents, which may be the same or different.

In one embodiment, the number of substituents on the cycloalkyl group isno greater than the number of carbon atoms in the cycloalkyl group.Thus, where the alkyl group is a C₆ alkyl group it may be substitutedwith no more than six substituents.

In one embodiment, the total number of carbon atoms in the cycloalkylgroup, together with the total number of carbon atoms present in —R⁶ and—R⁷ (where present) is at least 5, at least 6, at least 7 or at least 8.

In one embodiment, the cycloalkyl is cyclohexyl having a single hydroxylor —NR⁶R⁷ group, such as a 4-subsituted cyclohexyl group. In oneembodiment, the cycloalkyl is cyclopentyl having a single hydroxyl or—NR⁶R⁷ group, such as a 2- or 3-subsituted cyclopentyl group.

In one embodiment, the cycloalkyl is unsubstituted. In this embodiment,the substituents are located on the linker -L²-L¹-, which accordinglycannot be a covalent bond.

In one embodiment, for example where the core of the compound of formula(I) is Polymyxin B, the group G-L²-L¹- is not 2-aminocyclohexyl,3-aminocyclohexyl or 4-aminocyclohexyl.

For the avoidance of doubt, “cycloalkyl” refers to a group (1) which hasa ring system comprising one ring or two or more fused rings, whereinone ring of the fused ring system may be an aromatic ring, and (2) whichis attached to the rest of the molecule by a non-aromatic ring atom(i.e., a ring atom that is part of a non-aromatic ring that is part ofthe ring system). For example: cycloalkyl is an example of a C6cycloalkyl group; and tetralin-2-yl is an example of a Cio cycloalkylgroup.

Where an aromatic ring is present, it may be optionally substituted. Theoptional substituents are those described as optional substituents forthe C₅₋₁₂ aryl group.

In one embodiment, where the cycloalkyl comprises two or more fusedrings, each ring is non-aromatic.

In one embodiment, the cycloalkyl group comprises one ring.

C₂₋₁₂ alkyl

The N terminal substituent of the polymyxin compound may be a C₂₋₁₂alkyl group (“alkyl group”). Thus, -G may be C₂₋₁₂ alkyl.

When -G is C₂₋₁₂ alkyl, -L¹- may be a covalent bond or C₂₋₁₀heteroalkylene, such as a covalent bond.

When -G is C₂₋₁₂ alkyl, -L²- may be a covalent bond or C₄₋₁₂heterocyclyl, for example a covalent bond.

In one embodiment, where -G is C₂₋₁₂ alkyl, both -L²- and -L¹⁻ arecovalent bonds. Thus, -G is connected directly to —X—.

In one embodiment, C₂₋₁₂ alkyl is C₃₋₁₂ alkyl, for example C₄₋₁₂ orC₆₋₁₂ alkyl.

In one embodiment, C₂₋₁₂ alkyl is C₂₋₆ alkyl, for example C₂₋₄ alkyl.

The alkyl group is a saturated, aliphatic alkyl group. The alkyl groupmay be a linear or a branched alkyl group.

In one embodiment, the alkyl group is branched and the branch is not atthe carbon atom that is a to the group -L²-, -L¹-, or —X—.

In one embodiment, the number of substituents on the alkyl group is nogreater than the number of carbon atoms in the alkyl group. Thus, wherethe alkyl group is a C₂ alkyl group it may be substituted with no morethan two substituents.

In one embodiment, the total number of carbon atoms in the alkyl group,together with the total number of carbon atoms present in —R⁶ and —R⁷(where present) is at least 5, at least 6, at least 7 or at least 8.

In one embodiment, the alkyl group has a substituent at the terminalcarbon. Terminal carbon refers to a carbon atom that would be a —CH₃ ifit bore no substituents. In a branched alkyl group this carbon may bethe carbon atom that is at the terminal of the longest linear portion ofthe alkyl group.

In one embodiment, the alkyl group has a substituent that is located ata carbon atom that is β or γ the terminal carbon atom.

As noted above, in one embodiment, a —NR⁶R⁷ group, where present as asubstituent to the alkyl group, is a substituent to a carbon atom thatis not α to the group -L²-, -L¹-, or —X—. As noted above, in oneembodiment, a hydroxyl group, where present as a substituent to thealkyl group, is a substituent to the carbon atom a to the group -L²-,-L¹-, or —X—.

In one embodiment, the alkyl group has no substituent at the carbon atoma to the group -L²-, -L¹-, or —X—.

In one embodiment, the alkyl, if substituted, has a maximum of one ortwo substituents, which may be the same or different.

In alternative aspects of the present invention, the N terminalsubstituent of the polymyxin compound is a C₁₋₁₂ alkyl group. In oneembodiment, —R⁵ is C₁₋₁₂ alkyl group, such as C₁ alkyl. Where —R⁵ is C₁alkyl, one substituent is present, such as one —NR⁶R⁷ group.

C₅₋₁₂ aryl

The N terminal substituent of the polymyxin compound may include or be aC₅₋₁₂ aryl group (“a group”). Thus, -G may be C₅₋₁₂ aryl.

When -G is C₅₋₁₂ aryl, -L¹- may be a covalent bond, C₁₋₁₂ alkylene orC₂₋₁₀ heteroalkylene, for example a covalent bond or C₁₋₁₂ alkylene.

When -G is C₅₋₁₂ aryl, -L²- may be a covalent bond or C₄₋₁₂heterocyclyl, for example a covalent bond.

The aryl group is optionally substituted, with these substituents beingin addition to any hydroxyl or —NR⁶R⁷ groups.

In one embodiment, C₅₋₁₂ aryl is C₅₋₇ aryl

In one embodiment, C₅₋₁₂ aryl is C₆₋₁₀ carboaryl or C₅₋₁₂ heteroaryl.

In one embodiment, C₅₋₁₂ aryl is C₆₋₁₀ carboaryl.

In one embodiment, C₆₋₁₀ carboaryl is phenyl or napthyl.

In one embodiment, C₆₋₁₀ carboaryl is phenyl.

In one embodiment, C₅₋₁₂ aryl is C₅₋₁₂ heteroaryl, for example C₅₋₁₀,C₅₋₆, C₅ or C₆ heteroaryl.

The heteroaryl may contain one or two nitrogen atoms and additionally oralternatively, where the heteroaryl is a C₅ heteroaryl, it may containan oxygen or sulfur atom

In one embodiment, C₅₋₁₂ heteroaryl is independently furanyl, thienyl,pyrrolyl, imidazolyl, pyrazolyl, oxazolyl, isoxazolyl, thiazolyl,isothiazolyl, pyridyl, pyrimidinyl, pyrazinyl, pyridazinyl, quinolinyl,isoquinolinyl or indole. Additionally or alternatively, the C₅₋₁₂heteroaryl is independently pyridone.

Where a heteroaryl is present in group -G it is connected to -L¹-, -L²-or —X— via a ring carbon atom or a ring N atom, where present. In oneembodiment, the heteroaryl is connected via a ring carbon atom. Inanother embodiment, the heteroaryl is connected via a ring nitrogenatom, where present.

In one embodiment, C₅₋₁₂ aryl is phenyl or pyridine.

For the avoidance of doubt, “heteroaryl” refers to a group (1) which hasone or more heteroatoms (e.g., N, O, S) forming part of a ring system,wherein the ring system comprises one ring or two or more fused rings,wherein at least one ring of the ring system is an aromatic ring, and(2) which is attached to the rest of the molecule by an aromatic ringatom (i.e., a ring atom that is part of an aromatic ring that is part ofthe ring system). For example: pyridyl is an example of a C₆heteroarylgroup; isoquinolyl is an example of a C₁₀heteroaryl group; and1,2,3,4-tetrahydro-isoquinoline-7-yl is an example of a C₁₀heteroarylgroup.

Where a non-aromatic ring is provided, it has no optional substituents(though it may be provided with one or more hydroxyl or —NR⁶R⁷ groups).

In one embodiment, where a heteroaryl comprises two or more fused rings,each ring is an aromatic ring.

In one embodiment, the heteroaryl group comprises one aromatic ring.

A heteroaryl group may also include a pyridonyl group, which may beregarded as a structure corresponding to a pyridinyl group having a 2-or 4- hydroxyl substituent.

Similarly, “carboaryl” refers to a group (1) which has a ring systemcomprising one ring or two or more fused rings, wherein at least onering of the ring system is an aromatic ring, and (2) which is attachedto the rest of the molecule by an aromatic ring atom (i.e., a ring atomthat is part of an aromatic ring that is part of the ring system). Forexample: phenyl is an example of a C₆ carboaryl group; and tetralin-6-ylis an example of a C₁₀ carboaryl group.

In one embodiment, where a carboaryl comprises two or more fused rings,each ring is an aromatic ring.

Where a non-aromatic ring is present, that ring may be a carbocycle(such as shown above for tetralin), or the ring may be a heterocycle, asshown below for the group dihydrobenzo[b][1,4]dioxin-6-yl.

In one embodiment, C₆₋₁₂ aryl is not diaminophenyl, such as3,5-diaminophenyl, for example when —X— is —C(O)— and when -L¹- and -L²-and are both covalent bonds.

In one embodiment, C₅₋₁₂ aryl is not trihydroxyphenyl, such as3,4,5-trihydroxyphenyl, for example when —X— is —C(O)—.

It is noted that Sandow et al. describe Polymyxin octapeptides having amodified N terminal. The N terminal group contains a phenyl group thatis optionally substituted by 1, 2 or 3 identical or different groupsselected from hydroxyl, alkoxy, amino, carboxyl, alkylamino and halogen.The phenyl group may be linked to the N terminal via an alkylene pacerand/or an imino oxime group. Alternatively, the N terminal groupcontains a 2-aminothiazol-4-yl group.

The worked examples in Sandow et al. are limited to octapeptides havinga 2-aminothiazol-4-yl group, a benzyl group or a 3,4,5-trihydroxyphenylgroup. There are no examples where a nonapeptide or decapeptide areused, and there are no examples where the N terminal group containsamino functionality.

It is noted that WO 2012/168820 describes Polymyxin decapeptides havinga modified N terminal. The publication suggests that the N terminalgroup could include aryl, aralkyl, heteroaryl and heteroaralkylfunctionality, amongst other options. Aryl and heteroaryl groups may belinked to another aryl or heteroaryl group, amongst other options. Thelinker may be a bond, —(CH₂)_(n)—, —(CH₂)_(n)—O—(CH₂)_(p)—,—(CH₂)_(n)—S—(CH₂)_(p)—, or —(CH₂)_(n)—NR³—(CH₂)_(p)—, where n is 0, 1,2 or 3; and p is 0, 1, 2 or 3; and R³ is H or CH₃.

The worked examples in WO 2012/168820 are limited to compounds where onearyl or heteroaryl group is linked directly to another aryl orheteroaryl group. There are no examples where a linker is present.

Aryl Group Substituents

The group —R⁵ may include an aryl group, for example where -G is C₅₋₁₂aryl or C₃₋₁₀ cycloalkyl contains a fused aromatic ring, or where -D isC₄₋₁₀ heterocyclyl containing a fused aromatic ring.

Each aryl group is optionally substituted with one or more substituents.

Where the aryl group is optionally substituted, there may be one, two orthree optional substituents.

Where a heteroaryl group is substituted, the substituents may beprovided on a ring carbon atom, for example an aromatic ring carbonatom.

Each optional substituent is selected from the list consisting of —C₁₋₄alkyl, halo, —CN, —NO₂, —CF₃, —NR¹⁰C(O)R¹⁰, —CON(R¹⁰)₂, —COORS, —OCOR¹⁰,—NR¹⁰COOR¹⁰, —OCON(R¹⁰)₂, —OCF₃, —NR¹⁰CON(R¹⁰)_(2,) —OR⁹, —SR⁹,—NR¹⁰SO₂R¹⁰, —SO₂N(R¹⁰)₂ and —SO₂R¹⁰ where each —R⁹ is independently—C₁₋₄ alkyl and each —R¹⁰ is independently —H or —C₁₋₄ alkyl

In one embodiment, each optional substituent is independently selectedfrom —C₁₋₄ alkyl, halo, —NR¹⁰C(O)R¹⁰, —CON(R¹⁰)_(2,) —COOR⁹, —OCOR¹⁰,—NR¹⁰COOR¹⁰, —OCON(R¹⁰)₂, —OCF₃, —NR¹⁰CON(R¹⁰)₂, —OR⁹, and —SR⁹, whereeach —R⁹ is independently —C₁₋₄ alkyl and each —R¹⁰ is independently —Hor —C₁₋₄ alkyl.

In one embodiment, each optional substituent is independently selectedfrom —C₁₋₄ alkyl and halo.

In one embodiment, a halo group is —F, —Cl or —Br.

In one embodiment, where a nitrogen atom is provided in an aromaticring, it may be optionally substituted with —R⁹ or —R¹⁰, whereappropriate.

The optional substituents may include a C₁₋₄ alkyl group, e.g. —R⁹ or—R¹⁰, either alone or as part of a larger substituent group. It is notedthat each C₁₋₄ alkyl group present may be substituted with the one, twoor three hydroxyl and/or —NR⁶R⁷ groups.

In one embodiment, —R⁹ or —R¹⁰ are not substituted with a hydroxyl or—NR⁶R⁷ group.

—R⁶ and —R⁷

In one embodiment, each —R⁶ and —R⁷, where present, is H.

In one embodiment, —R⁶ is H and —R⁷ is alkyl, such as methyl or ethyl,such as methyl.

In one embodiment, —R⁶ is methyl or ethyl, such as methyl.

Where -G is an aryl or cycloalkyl group, —R⁶ and —R⁷ may together withthe nitrogen atom form a heterocycle, for example C₄₋₁₀ heterocyclyl.

In one embodiment, the C₄₋₁₀ heterocyclyl contains one or twoheteroatoms selected from N, S and O. Where a S atom is present, it maybe in the form S, S(O) or S(O)_(2.) Where an N atom is present it me bein the form NH or NR, where R is C₁₋₄ alkyl, such as methyl or ethyl. Inone embodiment, the C₄₋₁₀ heterocyclyl is piperidinyl, piperazinyl,morpholinyl, dioxanyl, thiomorpholinyl (including oxidisedthiomorpholinyl), or pyrroldinyl.

In one embodiment, the C₄₋₁₀ heterocyclyl is piperidinyl, piperazinyl,thiomorpholinyl (including oxidised thiomorpholinyl), pyrroldinyl ormorpholinyl.

In one embodiment, the C₄₋₁₀ heterocyclyl is piperidinyl, piperazinyl orpyrroldinyl.

In one embodiment, one group —NR⁷R⁸, where present, is a guanidinegroup, such as —NHC(NH)NH₂.

—R⁹

In one embodiment, —R⁹ is methyl or ethyl.

In one embodiment, —R⁹ is methyl.

—R¹⁰

In one embodiment, —R¹⁰ is —H.

In one embodiment, —R¹⁰ is methyl or ethyl.

In one embodiment, —R¹⁰ is methyl.

REFERENCES

All documents mentioned in this specification are incorporated herein byreference in their entirety.

de Visser et al, J. Peptide Res, 61, 2003, 298-306

Dewitt et al. Org. Biomol. Chem. 2011, 9, 1846

GB 1421020.7

GCC 2012/22819

Ghose et al. J. Phys. Chem. A, 1998, 102, 3762-3772

Handbook of Pharmaceutical Excipients, 5th edition, 2005

Katsuma et al. Chem. Pharm. Bull. 2009; 57, 332-336

Petrosillo et al. Clin. Microbiol. Infect. 2008; 14, 816-827

Quale et al. Microb. Drug Resist. 2012; 18, 132-136

Remington's Pharmaceutical Sciences, 18th edition, Mack PublishingCompany, Easton, Pa., 1990

Sato et al. Chem. Pharm. Bull. 2011; 59, 597-602

Telkov et al. ACS Chemical Biology 2014, 9, 1172

TW 101142961

U.S. Pat. No. 8,415,307

Vaara et al, Antimicrob. Agents and Chemotherapy, 52, 2008. 3229-3236

Vaara et al. Microbiol. Rev. 1992; 56, 395-411

Velkov et al. ACS Chemical Biology, 2014, 9, 1172

WO 1988/00950

WO 2008/017734

WO 2010/075416

WO 2012/168820

WO 2013/072695

WO 2014/188178

WO 2015/135976

Yamada et al, J. Peptide Res. 64, 2004, 43-50

Yousef et al., Antimicrob. Agents Chemother. 2011, 55, 4044-4049

1. A compound of formula (I):

wherein: -T is R^(T)-X—; -A¹- is absent or is an amino acid residue;-A²- is an amino acid residue selected from threonine and serine, suchas L-threonine and L-serine; -A³- is an amino acid residue representedby:

where the asterisk is the point of attachment to -A²-, and —R³ is C₁₋₆alkyl, such as C₁₋₄, having one amino or one hydroxyl substituent; —X—is —C(O)—, —NHC(O)—, —OC(O)—, —CH₂— or —SO₂—; —R^(T) is a terminal groupcontaining hydroxyl and/or amino functionality, and where -A¹- isabsent, R^(T)-X— is not an α-amino acid residue having a free α-aminogroup (—NH₂), where the α-amino acid residue is selected from the groupconsisting of Ala, Ser, Thr, Val, Leu, Ile, Pro, Phe, Tyr, Trp, His,Lys, Arg, α,γ-diaminobutyric acid (Dab) and α,β-diaminopropionic acid(Dap); —R⁶ together with the carbonyl group and nitrogen alpha to thecarbon to which it is attached is an amino acid residue; —R⁷ togetherwith the carbonyl group and nitrogen alpha to the carbon to which it isattached is an amino acid residue; and —R⁶ together with the carbonylgroup and nitrogen alpha to the carbon to which it is attached is not aphenylalanine, leucine or valine residue and/or —R⁷ together with thecarbonyl group and nitrogen alpha to the carbon to which it is attachedis not a leucine, iso-leucine, phenylalanine, threonine, valine ornor-valine residue; R¹⁰ together with the carbonyl group and nitrogenalpha to the carbon to which it is attached, is a threonine or leucineresidue; and salts, solvates, protected forms and/or prodrug formsthereof.
 2. The compound of claim 1, wherein —R⁶ together with thecarbonyl group and nitrogen alpha to the carbon to which it is attachedis not a phenylalanine, leucine or valine residue.
 3. The compound ofclaim 2, wherein —R⁷ together with the carbonyl group and nitrogen alphato the carbon to which it is attached is a leucine, iso-leucine,phenylalanine, threonine, valine or nor-valine residue.
 4. The compoundof claim 1, wherein —R⁶ is C₁₋₁₂ alkyl, C₀₋₁₂ alkyl(C₃₋₁₀ cycloalkyl),C₀₋₁₂ alkyl(C₃₋₁₀ heterocyclyl) or C₀₋₁₂ alkyl(C₅₋₁₀ aryl), where theC₁₋₁₂ alkyl, C₃₋₁₀ cycloalkyl group C₃₋₁₀ heterocyclyl group, and theC₅₋₁₀ carboaryl group are optionally substituted.
 5. The compound ofclaim 4, wherein —R⁶ is C₀₋₁₂ alkyl(C₅₋₁₀ aryl), where the C₅₋₁₀carboaryl group is optionally substituted. 6-7. canceled
 8. The compoundof claim 5, wherein the C₅₋₁₀ aryl group is substituted with one or moregroups —R^(Z), where each group —R^(Z) is selected from halo, optionallysubstituted C₁₋₁₂ alkyl, optionally substituted C₂₋₁₂ alkenyl,optionally substituted C₂₋₁₂ alkynyl, optionally substituted C₃₋₁₀cycloalkyl, optionally substituted C₃₋₁₀ heterocyclyl, optionallysubstituted C₅₋₁₂ aryl, —CN, —NO₂, —OR^(Q), —N(R^(W))C(O)R^(Q),—N(R^(Q))₂, and —C(O)N(R^(Q))₂, where —R^(W) is H or C₁₋₄ alkyl; and—R^(Q) is H or —R^(Q1), and —R^(Q1) is selected from optionallysubstituted C₁₋₁₂ alkyl, C₂₋₁₂ alkenyl, C₂₋₁₂ alkynyl, and C₅₋₁₂ aryl,and in a group —N(R^(Q))₂ the groups —R^(Q) may together with thenitrogen atom to which they are attached form a C₅₋₆ heterocycle, wherethe heterocycle is optionally substituted. 9-15. canceled
 16. Thecompound of claim 5, wherein C₀₋₁₂ alkyl(C₅₋₁₀ aryl) is C₁ alkyl(C₅₋₁₀aryl).
 17. The compound of claim 4, wherein —R⁶ is C₀₋₁₂ alkyl(C₃₋₁₀cycloalkyl), where the C₃₋₁₀ cycloalkyl group is optionally substituted.18. canceled
 19. The compound of claim 17, wherein the C₃₋₁₀ cycloalkylgroup is unsubstituted.
 20. The compound of claim 17, wherein the C₃₋₁₀cycloalkyl group is substituted with one or more groups —R^(Z), whereeach group —R^(Z) is selected from halo, optionally substituted C₁₋₁₂alkyl, optionally substituted C₂₋₁₂ alkenyl, optionally substitutedC₂₋₁₂ alkynyl, optionally substituted C₃₋₁₀ cycloalkyl, optionallysubstituted C₃₋₁₀ heterocyclyl, optionally substituted C₅₋₁₂ aryl, —CN,—NO₂, —OR^(Q), —SR^(Q), —N(R^(W))C(O)R^(Q), —N(R^(Q))₂, and—C(O)N(R^(Q))₂, where —R^(W) is H or C₁₋₄ alkyl; and —R^(Q) is H or—R^(Q1), and —R^(Q1) is selected from optionally substituted C₁₋₁₂alkyl, C₂₋₁₂ alkenyl, C₂₋₁₂ alkynyl, and C₅₋₁₂ aryl, and in a group—N(R^(Q))₂ the groups —R^(Q) may together with the nitrogen atom towhich they are attached form a C₅₋₆ heterocycle, where the heterocycleis optionally substituted.
 21. The compound of claim 17, wherein C₀₋₁₂alkyl(C₃₋₁₀ cycloalkyl) is C₁ alkyl(C₃₋₁₀ cycloalkyl).
 22. The compoundaccording to claim 4, wherein —R⁶ is optionally substituted C₁₋₁₂ alkyl.23-24. canceled
 25. The compound according to claim 1, wherein: (i) -A¹-is absent; and/or (ii) A²- is L-threonine or L-serine; and/or (iii) R³together with the carbonyl group and nitrogen alpha to the carbon towhich it is attached, is α,γ-diaminobutyric acid (Dab) or α,62-diaminopropionic acid (Dap); and/or (iv) R¹⁰ together with the carbonylgroup and nitrogen alpha to the carbon to which it is attached is athreonine residue, such as L-threonine; and/or (v) X— is —C(O)—. 26-31.canceled
 32. The compound according to claim 1, wherein —R^(T) is anamino-containing group:

where: —R^(A) is hydrogen or -L^(A)-R^(AA); -Q- is a covalent bond or—CH(R^(B))—; —R^(B) is hydrogen or -L^(B)-R^(BB); or, where -Q- is—CH(R^(B))—, —R^(A) and —R^(B) together form a 5- to 10-memberedmonocyclic or bicyclic carbocycle, or —R^(A) and —R^(B) together form a5- to 10-monocyclic or bicyclic heterocycle; and, where -Q- is acovalent bond —R^(A) is -L^(A)-R^(AA), and where -Q- is —CH(R^(B))— oneor both of —R^(A) and —R^(B) is not hydrogen; —R¹⁶ is independentlyhydrogen or C₁₋₄ alkyl; —R¹⁷ is independently hydrogen or C₁₋₄ alkyl; or—NR¹⁶R¹⁷ is a guanidine group; or —R¹⁷ and —R^(A) together form a 5- to10-membered nitrogen-containing monocyclic or bicyclic heterocycle; or,where -Q- is —CH(R^(B))—, —R¹⁷ and —R^(B) together form a 5- to10-membered nitrogen-containing monocyclic or bicyclic heterocycle; andwhere —R¹⁷ and —R^(A) together form a monocyclic nitrogen-containingheterocycle, each ring carbon atom in —R¹⁷ and —R^(A) is optionallymono- or di-substituted with —R^(C), and the monocyclic heterocycle issubstituted with at least one group selected from —R^(C), —R^(N),—R^(NA) and -L^(B)-R^(BB), where present, and where —R¹⁷ and —R^(B)together form a monocyclic nitrogen-containing heterocycle, each ringcarbon atom in —R¹⁷ and —R^(B) is optionally mono- or di-substitutedwith —R^(C), and the monocyclic heterocycle is substituted with at leastone group selected from —R^(C), and —R^(N), where present, or themonocyclic heterocycle is optionally substituted when —R^(A) is-L^(A)-R^(AA), and a monocyclic nitrogen-containing heterocycleoptionally contains one further nitrogen, oxygen or sulfur ring atom,and where a further nitrogen ring atom is present it is optionallysubstituted with —R^(N), with the exception of a further nitrogen ringatom that is connected to the carbon that is a to the group —X—, whichnitrogen ring atom is optionally substituted with —R^(NA); where —R¹⁷and —R^(A) or —R¹⁷ and —R^(B) together form a bicyclicnitrogen-containing heterocycle, each ring carbon atom in —R¹⁷ and—R^(A) or —R¹⁷ and —R^(B) is optionally mono- or di-substituted with—R^(D); and the bicyclic nitrogen-containing ring atom heterocycleoptionally contains one, two or three further heteroatoms, where eachheteroatom is independently selected from the group consisting ofnitrogen, oxygen and sulfur, and where further nitrogen ring atoms arepresent, each further nitrogen ring atom is optionally substituted with—R^(N), with the exception of a nitrogen ring atom that is connected tothe carbon that is a to the group —X—, which nitrogen ring atom isoptionally substituted with —R^(NA); where —R^(A) and —R^(B) togetherform a 5- to 10-membered monocyclic carbocycle or heterocycle, each ringcarbon atom in —R^(A) and —R^(B) is optionally mono- or di-substitutedwith —R^(C), and a nitrogen ring atom, where present in the monocyclicheterocycle, is optionally substituted with —R^(N), with the exceptionof a nitrogen ring atom that is connected to the carbon that is a to thegroup —X—, which nitrogen ring atom is optionally substituted with—R^(NA); where —R^(A) and —R^(B) together form a 5- to 10-memberedbicyclic carbocycle or heterocycle, each ring carbon atom in —R^(A) and—R^(B) is optionally mono- or di-substituted with —R^(D), and a nitrogenring atom, where present in the bicyclic heterocycle, is optionallysubstituted with —R^(N), with the exception of a nitrogen ring atom thatis connected to the carbon that is a to the group —X—, which nitrogenring atom is optionally substituted with —R^(NA); and where R¹⁷ and—R^(A) or —R¹⁷ and —R^(B) together form a 5- to 10-memberednitrogen-containing monocyclic or bicyclic heterocycle, or where —R^(A)and —R^(B) together form a 5- to 10-membered monocyclic or bicycliccarbocycle, or together form a 5- to 10-membered monocyclic or bicyclicheterocycle, a carbon ring atom in —R¹⁷ and —R^(A), —R¹⁷ and —R^(B), or—R^(A) and —R^(B) is optionally alternatively substituted with oxo (═O);each —R^(C) is independently -L^(C)-R^(CC); each —R^(D) is independentlyselected from —R^(C), halo, —NO₂, —OH, and —NH₂; each —R^(N) isindependently -L^(N)-R^(NN); each —R^(NA) is independently —R^(L)—R^(NN)or —R^(NN); —R^(AA), —R^(BB), and each —R^(CC) and —R^(NN) wherepresent, is independently selected from C₁₋₁₂ alkyl, C₃₋₁₀ cycloalkyl,C₄₋₁₀ heterocyclyl, and C₅₋₁₂ aryl; each -L^(A)- is independently acovalent bond or a linking group selected from —R^(L)—*, —O-L^(AA)-*,—OC(O)-L^(AA)-*, —N(R¹¹)-L^(AA)-*, and —C(O)-L^(AA)-*, where theasterisk indicates the point of attachment of the group -L^(A)- to—R^(AA); each -L^(B)- and -L^(C)- is independently a covalent bond or alinking group selected from —R^(L)—*, —O-L^(AA)-*, —OC(O)-L^(AA)-*,—N(R¹¹)-L^(AA)-*, —N(R¹¹)C(O)-L^(AA)-*, —C(O)-L^(AA)-*, —C(O)O-L^(AA)-*,and —C(O)N(R¹¹)- L^(AA)-* and optionally further selected from—N(R¹¹)S(O)-L^(AA)-*, —N(R¹¹)S(O)₂-L^(AA)-*, —S(O)N(R¹¹)-L^(AA)-*, and—S(O)₂N(R¹¹)-L^(AA)-* where the asterisk indicates the point ofattachment of the group -L^(B)- to —R^(BB) or the group -L^(C)- to—R^(CC); each -L^(N)- is independently a covalent bond or a groupselected from —S(O)-L^(AA)-*, —S(O)₂-L^(AA)-*, —C(O)-L^(AA)-* and—C(O)N(R¹¹)-L^(AA)-*, where the asterisk indicates the point ofattachment of the group -L^(N)- to —R^(NN); and each -L^(AA)- isindependently a covalent bond or —R^(L)—; and each —R^(L)- isindependently selected from C₁₋₁₂ alkylene, C₂₋₁₂ heteroalkylene, C₃₋₁₀cycloalkylene and C₅₋₁₀ heterocyclylene, and where -L^(AA)- is connectedto a group C₁₋₁₂ alkyl, —R^(L)- is not C₁₋₁₂ alkylene; and each C₁₋₁₂alkyl, C₃₋₁₀ cycloalkyl, C₄₋₁₀ heterocyclyl, C₅₋₁₂ aryl, C₁₋₁₂ alkylene,C₂₋₁₂ heteroalkylene, C₃₋₁₀ cycloalkylene and C₅₋₁₀ heterocyclylenegroup is optionally substituted, where —R^(S) is an optional substituentto carbon and —R¹² is an optional substituent to nitrogen; each —R^(S)is independently selected from —OH, —OR¹², —OC(O)R¹², —OC(O)R¹², halo,—R¹², —NHR¹², —NR¹²R¹³, —NHC(O)R¹², —N(R¹²)C(O)R¹², —SH, —SR¹²,—C(O)R¹², —C(O)OH, —C(O)OR¹², —C(O)NH_(2,) —C(O)NHR¹² and C(O)NR¹²R¹³,except that —R¹² is not a substituent to a C₁₋₁₂ alkyl group; or where acarbon atom is di-substituted with —R^(S), these groups may togetherwith the carbon to which they are attached form a C₃₋₆ carbocycle or aC₅₋₆ heterocycle, where the carbocycle and the heterocycle areoptionally substituted with one or more groups —R¹²; each —R¹² isindependently C₁₋₆ alkyl, C₁₋₆ haloalkyl, phenyl or benzyl; each —R¹³ isindependently C₁₋₆ alkyl, C₁₋₆ haloalkyl, phenyl or benzyl; or —R¹² and—R¹³, where attached to N, may together form a 5- or 6-memberedheterocyclic ring, which is optionally substituted with C₁₋₆ alkyl, C₁₋₆haloalkyl, phenyl or benzyl; each —R¹¹ is independently hydrogen or C₁₋₄alkyl.
 33. A compound of formula (II):

wherein: -T^(A) is hydrogen, C₁₋₄ alkyl or R^(N)—X—; -A¹- is absent oris an amino acid residue; -A²- is absent or is an amino acid residue;-A³- is absent or is an amino acid residue; —X— is —C(O)—, —NHC(O)—,—OC(O)—, —CH₂— or —SO₂—; —R^(N) is a terminal group; —R^(6A) is C₁₋₁₂alkyl, C₀₋₁₂ alkyl(C₃₋₁₀ cycloalkyl), C₀₋₁₂ alkyl(C₃₋₁₀ heterocyclyl) orC₀₋₁₂ alkyl(C₅₋₁₀ aryl), where the C₁₋₁₂ alkyl, C₃₋₁₀ cycloalkyl groupC₃₋₁₀ heterocyclyl group, and the C₅₋₁₀ aryl group are optionallysubstituted, with the proviso that —R^(6A) is not benzyl, iso-butyl,iso-propyl, 4-phenylphen-1-yl methyl, —(CH₂)₇CH₃, 4—(OBn)-phen-1-ylmethyl or —CH₂S(CH₂)₅CH₃; -R^(7A) together with the carbonyl group andnitrogen alpha to the carbon to which it is attached is an amino acidresidue; R¹⁰ together with the carbonyl group and nitrogen alpha to thecarbon to which it is attached, is a threonine or leucine residue; andsalts, solvates, protected forms and/or prodrug forms thereof.
 34. Thecompound according to claim 33, wherein —R^(6A) is: (i) —C₀₋₁₂alkyl(C₅₋₁₀ aryl), where the C₅₋₁₀ carboaryl group is optionallysubstituted; or (ii) C₀₋₁₂ alkyl(C₃₋₁₀ cycloalkyl), where the C₃₋₁₀cycloalkyl is optionally substituted. 35-43. canceled
 44. The compoundaccording to claim 33, wherein: (i) -A¹- is absent; and/or (ii) A²- isL-threonine or L-serine; and/or (iii) R³ together with the carbonylgroup and nitrogen alpha to the carbon to which it is attached, isα,γ-diaminobutyric acid (Dab) or α,β-diaminopropionic acid (Dap), suchas L-Dab or L-Dap; and/or (iv) R¹⁰ together with the carbonyl group andnitrogen alpha to the carbon to which it is attached is a threonineresidue, such as L-threonine-, and/or (v) X— is —C(O)—. 45-49. canceled50. The compound according to claim 33, wherein —R^(T) contains hydroxyland/or amino functionality.
 51. A pharmaceutical composition comprisinga compound according to claim 1 or a compound according to claim
 50. 52.canceled
 53. A method of treating a microbial infection in a patient,comprising administering compound according to claim 1 or a compoundaccording to claim 50 the method comprising the step of administering acompound of claim 1 or a compound of claim 15 to a patient in needthereof.
 54. canceled
 55. A method according to claim 53, wherein themicrobial infection is a Gram-negative bacterial infection. 56-73.canceled